Right, so if I go fly a plane with no training or testing it's ok, because I'll only do it once?
Vehicle inspections don't look at things that are damaging to the vehicle, they look at things that could endanger other drivers. As such, your check engine light comment is irrelevant, as is the oil changing. The emissions and brakes, sure, but guess what? Those are things the RIDERS will notice, and they will get bad rating for it and get deactivated before too long.
Further, lots of Uber drivers don't actually drive that much. Certainly not more than, say, someone who commutes in a major city, or who goes on road trips. If you are going to harp on this further, I would suggest a better system would be to have inspections based on miles driven, rather that periods of time elapsed.
And in any event, you are ignoring the elephant in the room, the enormously expensive medallions/good-old boy "regulations" that price everyone out of the market and create artificial scarcity.