Uber is selling unorganized, uninsured, unchecked drivers. I believe no legal taxi company can do that since they're liable would anything happen to you. If Uber had to form, insure, optimize, thus manage, they'd require additional workforce, time, costs, and wouldn't give it to you for free.
The customer interface is (was? I don't know if taxi companies competes on the app side) way above and that's the value here. Better information and information model, almost no idle time.