It seems like the only things they would need are energy and access to materials for luxury goods. Presumably they could mostly lock the "human economy" out of access to these things through control over AI weapons, but there would likely be a lot of arable land that isn't valuable to them.
Outside of malice, there doesn't seem to be much reason to block the non-technological humans from using the land they don't need. Maybe some ecological argument, the few AI-enabled elites don't want billions of humans that they no longer need polluting "their" Earth?
