> Intellectual stimulation, or goals that stretch one's abilities, don't have to come from work

Just different definitions of "work". I think the sense meant by those saying people "need work" is "meaningful toil". Something that requires focused effort, and done for some tangible purpose.

So cashier, janitor, waiter would fit that broad definition, even though they are not a focus of intellectual life. But there can be other types of work that also fulfill intellectual needs, that might be more fulfilling for many (most? all?) people.