The belief that the USSR fell apart because its economic system was unsustainable is deeply Marxist. Marxism’s central idea is that economic relations are the defining factor in everything.
However, as we can see in North Korea, Cuba and Venezuela, the complete and utter dysfunctionality of their economy only adds to the longevity of these regimes.
“People are going to get fed up with living in poverty and will overthrow the regime that tyrannizes them and doesn’t let them live better.” Oh, you, funny bunny. It’s the exact opposite. The hungrier and the more beaten down they are, the more they are prone to pout if anybody tries to liberate them.