I assume they probably don't care about how a random scummy startup works; they want no part in it, including the rigmarole for opting out (if one exists).

No, but if you manage to identify all of these delivery people and refuse them service I bet that they unlist you.

That's a fairly unreasonable assumption. Odds are the only thing a human at corporate will ever see is "Driver John Doe could not complete delivery, customer complained" Unless purely by chance the same person just so happens to see the same issue with the same restaurant a few times, it's very unlikely that they'ed notice a trend, nonetheless correctly deduce its cause. The person in charge of making sure deliveries get completed is almost certainly not the person handling restaurant partnerships.

Even if someone does eventually notice and takes corrective action, this is far from an optimal way to do it. Given that the server is acting like the drivers should just know that they wanted to be unlisted, it wouldn't surprise me if the "we told you before" means all they did was tell drivers they wanted to opt out and never actually did the opt out procedure.

I'm going to start showing up at your house and ringing the doorbell once a day until you follow my opt-out procedure.

If you hire a different kid everyday to ring my doorbell and don't tell them you've been pestering me for weeks, I'm not going to take it out on the kid.

Note I said every. It is very unlikely that you could manage it. But if their success rate for a particular store. dropped to zero I suspect they would notice sooner or later.

I also never said that it is a good way to accomplish this. I'm just pointing out that refusing the driver can be a way to get them to leave.