Tipping isn’t “almost mandatory”. People were happily driving Ubers before they even introduced the tipping feature in-app. My rating is based on taking hundreds of rides while living for years on both coasts, in CA and NJ. Out of all those rides only one driver (a horrible one, who took like three wrong turns in twenty minutes, with navigation) ever asked for a tip. I maintain my rating by being clean, polite, and punctual.