Subprime loans are expensive because they're risky. Nobody is stopping those people from taking the normal lease, except that they can't get one because they have bad credit.
The problem with the mortgage crisis was that banks were making loans to people they knew would default on them and then reselling the loans as AAA loans, and insurance companies selling credit-default swaps under the same assumption. Then suddenly everyone finds out that so many of the loans are garbage that it made huge institutions insolvent.
There is none of that going on here. Uber is just willing to take the risk of defaults for the benefit of having more drivers.
So everyone is stopping them.
I'm pretty anti-Uber, but that's not shocking given the unlimited mileage provision. My last car lease quoted additional mileage over the 10k/year at $0.21/mile, which'd add up extremely quickly as a taxi driver.