Uber and Lyft (and AirBnB, VRBO, and Homeaway) are also subsidized in many cases by “I already own an expensive asset and carry all the fixed costs already, so I just need to make a profit over marginal costs”, which is largely the same as people who take a second or hobby job (including teenagers babysitting).

That subsidy is structural, IMO. That we see a lot of full time AirBnBs and full time Uber/Lyft drivers may mean it’s sustainable even outside of VC support. (I have no inside information, but I suspect that ride-sharing is economically profitable long-term at current end-user prices in all established markets.)