That is not a generalization, that is actually a fact. Doordash and other delivery apps gradually added restaurants on their platforms and still add new ones regularly. The fact that this happened in itself is a proof that they didn’t have food delivery as an option before.
If you want more concrete data, you need to look at how McDonald’s did deliveries in Manhattan but not rest of the US until they partnered with food delivery apps. Most other fast food chains did not have their own delivery network either.
