But isn't that covered in the "willing to pay more for the service" bucket? I find tipping awkward to the point of being willing to pay more for alternatives that bundle an otherwise expected tip into the service's initial pricing.
As a driver, sometimes you need to go the extra mile (no pun intended). There are times I need to help passengers carry things, go through drive throughs, catch trains using offensive driving, stopping for drunk people to puke and even serving as a makeshift therapist. The option is there, obviously I don't expect a tip for a 5 minute ride.
This is exactly why I enjoy Lyft's option for tipping. Tipping is awkward if I have to fumble for cash and stuff it in the driver's hands. It's not awkward if I can just press a button and charge it to my credit card.