I agree with Tom, maybe because S America has such a large number of species that live harmoniously that its easier to do.
In Central and N America there are often only 1 or 2 cichlid species in a particular habitat, and each may be of a different genus.
I find I can keep 4 or 5 different S Americans together in a 6ft tank fairly easily.
below are Acarichthys heckelli, xCichlasoma ornatum, Crenicihla sp belly crawler, and Guianacara sp.

With Central and North Americans, hardly ever more than 2 species for any length of time.
Below, 4 xCichlasoma bocourti with 6 Chuco intermedia share a tank.

I tried to keep a female festae in the tank above, came in one day and it simply vanished, never to be seen again.