this dialect showed up because they were too retarded to learn what they copied properly

That's not how it works, mate. They copied the speech of the lower-class Southern overseers, who spoke like this because this was the dialect of the area they were from. No better, no worse, than standard English.

not because iz dey culcha. none of them sat down and thought "well, to represent the black community better, i will now speak like an ape"

Just out of curiosity: why do you talk like an ape by not using 'ye' for the nominative instead of 'you'?

Did you not learn English properly?