Well, a capitalist/imperialist world is literally our material conditions right now, should we just ignore that?

No, but this is what makes a state necessary in the first place... External conflicts aren't the only reason it didn't go "as planned" of course, but they are a big reason why, but that was part of the "planning". The silent assumption behind saying that the state will wither, is that eventually the revolution would have spread to the rest of Europe, which didn't happen of course. The issue is that no one has ever figured out a way that doesn't involve assuming state power which can be effectively maintain gains made for a long time and in a large scale, especially in today's environment.

but the USSR/China/Whoever hasn't ignored that fact?