Likely reasons why Creole is spoken by Blacks
While watching the movie Australia (2008) which features Hugh Jackman and Nicole Kidman , I noticed that the Australian Aboriginal people have a version of Creole that was introduced at the beginning of the movie and then later on as the narrator (young half caste boy) tells the story. Although I am aware that Creole of one form or another is spoken among some Africa, Caribbean and African-American groups, I was not aware that the Aboriginal people of Australia also spoke their version of Creole.
Every Black human group seems to speak Creole of one kind or another (after I did some further research). Among Black groups that still maintain their original language (Africans, Australian Aboriginals, Papuans , Torres Straits etc), the Creole is spoken hand-in-hand with their languages.
In Ghana where I grew up, Creole is spoken and understood by almost everyone (in an informal way) but particularly by those who do not have formal education. Young secondary school boys think it is 'cool' to be able to speak it, it allows them to be part of a group and to avoid being called "Daddy's boy" or "Daddy's child", which is seen among these teenagers as a derogatory title for those who are soft (i.e. a spoiled or pampered child). Even among those who speak perfect English, Creole is also understood (however there are those young teenagers who speak Creole whose English grammar is crap, they are often seen as dropouts). The cool kids speaking Creole have equivalents for English slang such as 'Dude' 'Dunce' and 'wicked'. Old Creole had words like 'massa' (for 'master') and the well known 'boss man'. I was surprised to hear the Australian Aboriginal kid in the movie Australia refer to Nicole Kidman as 'Mrs Boss'. In West Africa some of the old Creole expressions have been adopted by the new Creole speakers. I had the chance to learn the Ghanaian Creole version while in secondary school and sometimes use it when speaking mostly with old acquaintances who went through the government secondary schools. Technically, Creole is obsolete for an individual who has learned the proper usage of a specific language (previously spoken as Creole) as a result of having been correctly educated in the speech of that language.
I think Creole first developed as Europeans came into contact with Africans (in the case of these) not formally educated in the Western way. Africans who were then taken off as slaves and bunched together soon lost their original languages but kept the Creole because it was the first form of the master's language that was learnt . It must be remembered that Black slaves for a long time were not given formal education. This means that the Creole eventually became for them a new language replacing their various African languages, in an environment where because of a mixture of languages no one African language could be used to communicate with everyone.
But that still does not get to the heart of the issue. I think the heart of the issue is that Africans first learnt European languages using African grammatical rules. This is why Creole is spoken as a simplified version of European languages (for Africans the European languages of the colonizers were English, French and Portuguese; German and Italian didn 't 'stay' long enough to influence in a long lasting way, while the Dutch and the Scandinavians lost their holdings to Britain and France). The reason why I say this is because among those West Africans who speak Creole (just because it is now part of the history of these people) those who speak English-based Creole can understand each other, while those who speak French-based Creole can understand each other, although individuals may be have different African languages and originate from different African countries. For instance I can understand Cameronian Creole as well as Sierra Leonean Creole, as well as Nigerian and Liberian because these are all based on English. Sometimes it only takes a bit of careful listening to 'get it'. Those Africans who were colonized by the French also have their versions of Creole and with some effort they can understand each other, although they may be from different countries.
Why do I say that the formation of spoken Creole was originally based on African language grammatical rules? Because I have observed this with the Creole spoken in Ghana as well as the versions spoken in other African countries such as Sierra Leone. Before Europeans came into the picture African languages were constructed in a way that directly reflects what is observed. Let me use an example from my language, Akan ( Twi ). When someone is angry, the person may say Me bo efu (transl - 'my body hairs standing upright!') or M' eni abri (transl- 'my eyes ripe-red!). To go home, one may say Me ko fie (I go home). For the simplest of sentences there is no verbal conjugation, although conjugation does exist as well as other forms of more complex sentence constructions. The Creoles created based on how the locals spoke their African languages used simple sentence constructions.
What also happened with the creation of Creoles is that some connectives were included. A Sierra Leonian man who wants to say "I am going home!" will say 'I dey go na hose'. The most significant part of that last sentence are the three words 'I go hose', the ' dey ' and ' na ' are connectives which do not have any meaning, they are 'fillers'. So the very action-oriented sentence "I go hose" is perhaps a simple example of a Creole created that reflects rules from an African language.
So one can imagine a transition from indigenous African languages to really rudimentary European languages (first forms of Creole, those still spoken in Africa for historical reasons) to a mixture between indigenous African languages and European languages (Creole types found mostly in the Caribbean) to Creoles based almost solely on European languages but having some of the simplified grammatical rules based on African languages (such as Ebonics spoken by Black African Americans).
In the Caribbean, two important forms of Creole are spoken in Jamaica ( Patwah /Patois) and Haitian Creole. These reflect two European varieties (English and French). These two forms of Creole have developed into languages for the Blacks who lived there because they no longer had their African languages, while in Africa (at least I can speak for West Africa) the Creole is spoken only for historical purposes because Africans can still speak to each other in their respective African languages. In Brazil, their Creole is obviously based on Portuguese.
As far as the Caribbean is concerned, I am quite sure that at least for Jamaica, the Creole they speak is based on African language rules. While visiting Jamaica I listened carefully to the Patwah , the rhythm with which the language is spoken is similar to the rhythms in the Akan language. This is no surprise because a good number of Akan slaves were settled in Jamaica and some of the names for foodstuffs like yam and other names still bear the Akan names although in some cases the intonation is slightly different. In Suriname, their version of Creole is interspersed with so many Akan words that my theory is substantiated. Creole became their new language. You can imagine how surprised I was while sitting on a bus in London behind two teenage guys from Suriname speaking their Creole ( Akan mixed with Dutch) and picking out the words. I wasn 't able to make out all of what they were saying though.
So what about African-Americans? It is my theory that because one of the inherent nature of Blacks is to hold on to 'tradition' for so long (Blacks can be said to be human Earth-element-types), one of the ways African-Americans hold on to their tradition is to speak in the way their forefathers, the Africans, spoke! This is the root of Ebonics, which is in turn based on the simple grammatical rules of African languages. Of course, not everyone who speaks Ebonics has perfect English grammar or is well educated, just as it is in Ghana where there are some individuals who have crappy English grammar (could be for a number of reasons) but prefer speaking in the local Ghanaian creole.
I imagine a similar reason exists to explain the Creole of the Australian Aboriginals and other Melanesian people and I would be quite interested to have a discussion on this topic with some Natives from these areas or others who speak an indigenous language together with one or other kind of Creole.