A reasonable tip ensures that someone will accept your order. Nobody is forced to go pick your food up.
I did a bunch of ride-a-longs with my buddy during COVID. Watching him decide which orders to accept was fascinating. There are lots of variables, and a reasonable tip was a requirement.
It basically boiled down to how much money per mile.
Some shady people will put a $20 at first, but then change it to $0 after the food is delivered -- not based on bad or slow service, but because they are assholes. The $20 is to get a Dasher to accept the order quickly. Bait and switch.
A reasonable tip ensures that someone will accept your order. Nobody is forced to go pick your food up.
I member when restaurants employed drivers that actually delivered reliably without needing to bid for their attention first. Hard to forget since I was one of them!
Hourly pay was regular minimum wage instead of the server level chump change, and when using my own car I received an amount for wear and tear + gas. So in my case tips were actual tips on top of a living wage and even if nobody had tipped it would have been an alright job.
I can't imagine trying to do the same thing for only tips.
It isn't only tips. I opt to be paid by time + tips. In my area it is $18.50 per hour driven with tips. I average about $25-$28 per hour. The real issue is that getting to the point where you can just go work whenever you want is really rough because there isn't always a spot available.