You have an incorrect reading of history and economy. Basically none of the wealth and comfort we (regular people) enjoy were "gifted" or "left over" willingly by the owner class. Everything had to be fought for: minimum wage, reasonable weekly hours, safe workplaces, child labor, retirement, healthcare...
Now, ask yourself, what happens when workers lose the only leverage they have against the owner class: their labor? A capitalist economy can only function if workers are able to sell their labor for wages to the owner class, creating a sort of equilibrium between capital and work.
Once AI is able to replace a significant part of workers, 99% of humans on Earth become redundant in the eyes of the owner class, and even a threat to their future prosperity. And they own everything, the police and army included.