It's not about communism vs a free market, but about a change even more radical than that: leaving aside "made by a human" labeling, and even if there were no other changes to power structures or economies and no AI doom, what does a world look like if the cost of having something done falls to a few cents of electricity and its burden? Growing crops still takes a lot of land and other resources...

How could AI possibly lead to communism?

If humans remain in control of it, then how can it possibly lead to anything other than extreme oligarchy?