I've noticed that for small orders, Uber Eats/Doordash/etc will suggest flat values, usually larger than standard tip sizes compared to your order., sometimes over half the order price (and that's after they add fees to make small orders too expensive).
But in larger orders the suggested tip sizes suddenly are percentages, as opposed to large flat values and are usually closer to customary sizes. To me it sounds like they know tips are important for the drivers, and without tips there's barely going to be any takehome as those companies will take most of it themselves (and still be unprofitable), but as a solution the try to get users to enter large tip amounts.