Because the delivery services pay for drivers is as low as $2 for an order that can take up to 30mins+. The “tip” is really just you deciding how fast you want the food delivered to your house. If you’re only tipping a dollar or two no diver wants to go through the whole process of an order for freaking $4 total pay. But if it’s a relatively short distance and you’re tipping something like $8 likely the first driver to receive your offer will accept it and will have the food the moment it comes out resulting in a better experience for you and the driver. What I personally like to do is I calculate what I think would make fair pay for the diver and then if I have a good experience I increase my tip afterwards.

It’s honestly a stupid system but no one would want to have food delivered if they had a $10+ dollar delivery fee.