I've experienced cheap delivered food done well when in Bejing, and it's definitely a real thing. However if you tag a $10+ service/delivery/tip onto the bill, it kind of negates the "cheap" part of the experience.
The prices are higher (the same plus delivery plus tip) and the food comes cold and unless you’re ordering for a cold outdoor social visit you’re eating it alone/with the same company you see everyday. That’s a market that serves homebodies (I’m one half the time) and absolutely will fail for people who go out to eat and drink socially (me the other half of the time) when that becomes available again.
The market for cheap delivered food is much larger than sit down restaurants.
Covid just make more of the population comfortable with apps.