It's also Chiang Kai-shek and the Nationalist party's fault for being weak rulers who spent most of their time enriching themselves.

Communism only takes root in countries where it's seen as a "step up" from the status quo for the majority of people. The Nationalist's incredibly poor performance in World War II, and their tenuous grip on power to begin with, gave the Communists a platform to convince the masses that they were going to improve things.