Communism as described by Marx is a withering away of the government to natural human cooperation, not a government monopoly. In fact no step of socialism actually requires a government monopoly, which is why we say it’s only been tried in limited form
this. The reason communism sucks so much is bc monopolies suck - giving the government a monopoly over the whole economy is dumb. but corporate monopolies are just as dumb, suck just as much, and need to be broken up.