Capitalist ideology sees class as unavoidable and so it strives to make it meritocratic and unstable. This was a radical idea in an era of nobility or castes, but ultimately resulted in the merchant class basically seizing control of society.

Communism strives to eliminate it entirely, but you wind up with some leaders being insincere or incapable of letting go of power. But you also have the fact that it's difficult to completely eliminate class.