My guess is because Uber is subsidising the ride and providing convenient bill paying options.

I'm in London, and public transport is good enough for most journeys, and I loathe black cabs far more than I feel anything (except distrust) about Uber.

Uber works wherever I am in London, it's cheap enough (realistic compared to black cabs).

It's good enough, but not good enough that I'm fine with their various invasive activities. One not mentioned elsewhere is how they use both rider and driver mobiles as a kind of distributed cache/database. Which is the thing that started me off on "kill the background process", initially to spare my own data and battery.