That's the thing; calling for takeout is easy, the hard part is that most restaurants don't efficiently cook enough volume enough to justify the overhead of having dedicated delivery drivers.
The value proposition that has changed with the delivery apps is that lots of restaurants can share the cost of a large pool of drivers with an app that can sufficiently allocate routes. This isn't a proposition that has actually been profitable yet, though, and really the only thing that makes this situation unique is that we are now in an unprecedented situation where indoor dining is recommended against and in some cases heavily restricted or banned entirely. Presumably when restaurants are free to operate traditionally again they might not find having such a low-margin delivery arm so great, and they will leave. Anecdotally, some restaurants did this in my area when lockdowns were eased up.
The value proposition that has changed with the delivery apps is that lots of restaurants can share the cost of a large pool of drivers with an app that can sufficiently allocate routes. This isn't a proposition that has actually been profitable yet, though, and really the only thing that makes this situation unique is that we are now in an unprecedented situation where indoor dining is recommended against and in some cases heavily restricted or banned entirely. Presumably when restaurants are free to operate traditionally again they might not find having such a low-margin delivery arm so great, and they will leave. Anecdotally, some restaurants did this in my area when lockdowns were eased up.