As if the tip actually goes to the dashers.

Ubereats lets you set the tip after the delivery. afaik the others don't.

Should be illegal to prompt a tip before services are rendered, including at those POS machines that ask you up front to tip even a small amount.

So little of that is actually under the control of the courier. I did that for a little bit, and generally the drive from the restaurant to the customer was the shortest part. You get an order for a restaurant that hopefully you're close to, but maybe you aren't. You get there and maybe the food is ready, maybe it isn't. Maybe it's been sitting on a shelf for half an hour. Maybe traffic is heavy, maybe the GPS gives you shitty fucking directions. Maybe you ordered from the wrong restaurant and instead of being 5 minutes it's 20. Sure, there are shitty couriers, but 9 times out of 10 your food is cold or late because of circumstances outside of their control.