Well Bezos did actually state that he wants to turn Earth into a natural park.

But yeah, the robot armies don't need grain so why hike up the price of bread? Lack of grain makes those people resentful which means you need to deal with their anger. Sure, it can be dealt with but it's just cheaper to give the humans grain so they are docile. This is basic governance 101 that goes back to the romans (and further).

They also didn't slaughter all horses immediately. You can't eat that much horse meat anyways. It happened piece by piece.

The only good reason for an abrupt mass culling of the 99% (for a coldly calculating rich person with no empathy) would be game theory, i.e. them not being a contender for power any more. If there are no humans, there is nobody who can question the control of the 1%. It would be thus less about economics and more about power.

I am really rooting for the bottom 99%, myself being a part of it, but I really don't know what will happen to us.