Not sure exactly how things are setup now for the various apps, but a few years ago some of the apps would charge the restaurant for their delivery service (sometimes a set monthly cost, sometimes a set cost per delivery, sometimes a percentage) so the restaurants would often recoup that cost by increasing prices in the app.

Heck, Doordash has an entire support page for merchants about setting prices in the app and whether to have them marked up.
https://help.doordash.com/merchants/s/article/How-to-Maximize-Visibility-and-Order-Volume-on-DoorDash?language=en_US