If I spend an hour and a half prepping and cooking dinner, but I managed to buy that ingredients for $10 less than what I would spend at a restaurant, it's still cheaper to eat at the restaurant if I factor in the time I spent.
Just an addendum: if that time would have been spent, say, watching TV (and you are a healthy adult that doesn't have any psychological or physiological benefit from watching TV) then the time cost is possibly negligible.
Full time salaried workers can't easily convert additional time into money.
I think we do see PP's point with poorer people with horrendous commutes, part time inconsistent jobs, etc. Lot's of anguish about "food deserts" of course, but I think there is a larger reckoning that we simply need to reduce work and commutes before dual income people at all levels can afford to cook real food.
Aside from buffet-style, casual, fast-casual, fast-food, and street food outlets fit in the “prepared food without, or without as much of, the frivolity that simulates aristocracy”. It’s not exactly an underserved space.