DoorDash created the shop portal with no input from the store, and then put up incorrect prices. If that scenario still exists, they could still do this, but most of the time the store has some kind of deal with DoorDash so they would be responsible for pricing.

As for why fill the boxes, technically DoorDash would be the store's customer, so if you didn't give them what was ordered they could press the issue. It'd be hard to police, as the person making the DoorDash order wouldn't complain, but it adds a way things could fail.

Plus, the post said dough at that scale is practically free.