Because they have no need to sell, they have all the power they need without human labor, and so human labor will be cut accordingly. There will be a huge class of people useless to the labor market. We have this today, we call them homeless. That is how we currently treat people who cannot participate in the labor market. Why will it suddenly get better if corporations no longer need us.

Again this is in a scenario where ai is allowed to replace humans en mass, it’s assuming governments don’t find a way to amicably deal with the unemployment.