Because communism doesn't work for large, heterogenous groups
I hear a lot of variations of this "socialism can't work for a large heterogenous group" and its such a dumb lib brainworm. Its incredibly rascist for one (obviously too if you think about it for more than 1 second) and the population size argument is just nonsensical. The largest country in the world is communist and has a heterogenous population. The USSR had a large heterogenous population and that fact had nothing to do with the eventual dissolution, but did have much to do with its success