Doordash pays a driver $2.50 for each delivery. If you tip 5 dollars, that's $7.50.
If you're 10+ miles away from the restaurant your order will likely take longer for someone to grab it until it gets stacked with another order coming in your direction.
Nobody wants to get paid $7.50 then be stuck 10 miles away from another order to pick up. Which turns out to be 7.50 for 20 miles of driving, which just isn't very good.
Obviously your personal numbers could be different, but that's the gist of it. If you tip well, your order will usually not be delayed by the delivery driver, but only the restaurant.