It's possible they're looking at the long-term picture and investing heavily now to aggressively counter anything that looks like stricter regulation. If they capitulate in Austin today, then tomorrow they'll be railroaded into doing it everywhere else, which will end up costing them not-insignificant amounts of money and drivers over time. Having mandatory background checks also significantly raises the barrier to entry for casual carpoolers, which is a market that Uber is keen to capture.