Being a glorified taxi dispatcher probably isn't Uber's idea of a successful endgame. They desperately want to be a big player in the future of autonomous transportation and are clearly willing to bet the success of their taxi dispatching company to do so. Cutting their burn rate to a skeleton crew means giving up on that ambition and spending the rest of their 'life' as a reasonably successful company, with perhaps some modest profits, dispatching taxis via a phone app, and neither they nor their investors seem to want that.