I think he does pellik.
OP, if you mean 1.d4 nf6 2.c4 e6 3.nf3 c5 (benoni)
Its probably because the nimzo is much more positional in nature than the benoni, it makes more sense to play another very solid, positional defence such as the queens indian, bogo or QGD.
someone just played this c5 anti nizmo against me and i was pretty taken aback. i was fully expecting a standard modern benoni, no one has ever played this against me before. fortunately i think my opponent was also shocked that he wasn't playing a benoni and he blundered away a piece about two moves later!
Any thoughts on this would be much appreciated!