(1) Many of people's needs are physical. AI is not going to increase food production or manufacturing productivity by simply replacing human labor because these areas have already been revolutionized by automation.

(2) Even many "service occupations" need the body as much as the mind. We depend on the sensory abilities of doctors and nurses, as well as their hands.

(3) The counter to the above two would be some large advances in physical technology, say robots that can pick tomatoes or the kind of "advanced manufacturing" that Eric Drexler talked about.