When was the last the techno-industrialist elite class said "what we have is enough"?

In this scenario, the marginal cost of taking everything else over is almost zero. Just tell the AI you want it taken over and it handles it. You'd take it over just for risk mitigation, even if you don't "need" it. Better to control it since it's free to do so.

Allowing a competing human economy is resources left on the table. And control of resources is the only lever of power left when labour is basically free.

> Maybe some ecological argument

There's a political angle too. 7 (or however many it will be) billion humans free to do their own thing is a risky free variable.