I'd bet typical users live closer to the city center. I've been using uber and lyft a lot in Chicago, Austin, and Denver recently, and my average cost per ride is probably around $12.
I used to live in Zone1/2, and had 24 hour bus routes. So still ~an order of magnitude - 10GBP vs 1.50.
I'd forgotten about sharing with friends. Taxis certainly work out well there. Maybe that's it?
It's probably simply that I hate spending money! :)