I've got to say though - Uber seems like it pays much better than most courier services used to pay drivers to deliver things!
I tried working for one of them, once -- and quit within a week. During the lunch rush, they had us delivering boxed lunches to various locations where we were only compensated about $1.50 for each successful delivery. Since you had to seek out people, parking your vehicle and taking things into buildings to them, you wasted a lot of time too.
The vehicle maintenance is always a factor -- but for people doing these jobs part-time, I think most rationalize some of it away, so to speak. (If you drive your car or truck a lot for various activities, adding some Uber trips means at least you're offsetting the total cost of its operation by doing some things that actually bring in revenue. With or without the Uber driving, you were going to have items breaking down and wearing out anyway.) The fact is, vehicle purchases are terrible investments. They depreciate 20% the minute you drive a new one off the lot, and in many cases, keep plummeting in value based on nothing more than the whims of the buying public, as the years pass. Viewed that way? I guess ANY time you can drive one someplace and get paid something, you're lessening that overall bleeding of money.