as long as you've got enough order volume to keep a delivery driver consistently busy, that works fine and the apps are unnecessary. for a pizza restaurant, or anybody else focused on delivery orders, the apps aren't necessary

the utility of the apps is to distribute the load from multiple restaurants across a shared pool of delivery drivers, so a restaurant who otherwise wouldn't be able to offer delivery can tap into that labour pool for infrequent delivery orders. food delivery apps have greatly expanded the number of places that offer delivery. most restaurants simply didn't offer it before the apps.