>Why would you keep using an app that you suspect was cynically exploiting your generosity like that? I’d drive every time rather than encourage such behaviour.

Surely you already know that choosing things doesn't always simplify down to a single dimension. Instead, there are multiple factors that lead people to deliberately choose options that have negatives.

E.g. Why do people continue to use Ryanair airlines if they always nickel & dime customers and treat them like shit?!? Because the mistreatment by Ryanair is still better than driving for 6 hours or paying more $$$ for Air France or KLM.

Likewise, why do customers continue playing along with the tips/bribery/ransom game in the delivery app?!? Because the user-hostile app is still better than rounding up the small toddlers and infant into the car, fasten the car seat, and drive to the restaurant.

Life doesn't always provide unambiguous good options. Instead, you choose the "least bad" from the list of bad options.