well, the problem with that logic is when orders are rejected repeatedly time elapses. and once somebody finally agrees to pick it up and delivery it to you, you're assuming they are responsible for the delay. when an order bounces around unclaimed for an hour+ due to $0 tip, an extra reason to not accept the order is created; drivers dont want to deal with irate customers that believe they are responsible for the delay.
furthermore, delays in delivery more often then not have to do with the restaurant de-prioritizing online orders. speak to any delivery driver and ask about how long they wait and wait at restaurants and how customers seem to believe they're just lollygagging around. the fact is restaurants are to blame and drivers often have to remind them to actually cook the food.