Different water and different temperaments.
Water was pointed out before me, but as for temperaments...typically for Africans you want to overstock your tank (and have heavy filtration for this) where as CA/SA you want to have defined territories and will have a more understocked tank.
Africans if understocked will pick on the weakest fish until it's dead, then go onto the next weakest and etc. Overstocking ensures that the same fish isn't always getting harassed.
For SA/CA they will define and defend their specific territories so you need to have large spaces so each one can do this.
