I would like to point out that it wasn't exactly communist per se, that is, the Marxist revolution of the working class. Rather, Mao adapted 'communism' into an agrarian-centric revolution.

As to how it can be so popular in spite of pre existing ideologies like Confucianism, socio-economic factors played a huge role. Vast economic disparities, vividly experienced among the peasant class, gave an impetus to the movement. As a peasant like the vast majority, the perceived prospects of getting out of the dumps were naturally attractive.