[aflag]

The restaurant probably doesn't want the bad press associated with other customers getting cold/melted/soggy/etc food. Also, the restaurant may want to limit the amount of takeaway, as the venue may be small to accommodate too many carriers coming and going. Also, the courier may not like the route, maybe it takes too long (due to distance, but also traffic and other road conditions) and it's not worthwhile for them. The point is that you are just one piece of the equation and those apps are not necessarily telling you what you want, but telling you what they want.

[gruez]

Shouldn't those concerns be addressed by the restaurant itself, rather through various delivery platforms? After all, there's no real difference between you going to pick up the food yourself and you hiring a contractor to do it.

[aflag]

There is a difference. People are far less likely to go themselves, so that may be manageable by the restaurant. The app brings a lot more orders in. The restaurant possibly solved the problem by telling the delivery platform. If they suddenly had a bunch of couriers showing up at their door at peak times their solution would likely be similar, by telling the customer that they live too far away so they won’t let them order takeaway or something else along those lines. But the restaurants probably prefer to deal with a single party that can handle that bit of customer satisfaction for them.