It's stupid to have the tip box sitting there. I wonder if they could have a discrete sign? 'Cash tips appreciated, and preferred to ones left on the app?"
I've only used UBER a few times but tipped the drivers cash each time, and they seemed surprised. Both had mumbled about the low cost of the 'long trip' they got stuck with. ($80 and $90 runs, one to the airport one uber couldnt' pick up, the other to a city in the sticks the driver would have to run empty back from)