The reason tipping keeps popping up in new markets (like Uber/Lyft/Instacart/Doordash) is largely the same reason it's so hard to get rid of in existing industries: it allows businesses to advertise lower prices and lets customers actually pay those lower prices if they're willing to take the relatively minimal and sometimes even completely negligible social cost of not tipping.

Just look at how it went with Uber. Uber didn't want tipping to be part of the experience, but they kept lowering driver wages until drivers needed tips to survive and started rating down passengers who didn't offer cash tips. When the problem started becoming severe, they could have solved it by just upping driver wages. Instead, they kept fares impossibly low but added tipping into the app.