You need to keep in mind that we are stuck on this planet, and the super-intelligence is not; i'm not assuming that the super-intelligence will be any more benign than us; on the contrary the AI can go and burn resources left and right and eat Jupiter, it's pretty big and dense (dense means low lag if you somehow build computers inside of it). It's just that for AI to keep us, is easier than for entire mankind to keep 1 bonsai tree.

Also, we mankind as meta-organism are pretty damn short sighted.