Besides the apps, most cabs are far more crappy than the Uber cars. I feel unsafe in a lot of them even though the cab companies insist they conform better to safety regulations; in Thailand, China or Hong Kong, cabs are mostly such garbage; smelly, usually missing seat belts, horrible suspension, drivers rude and not very good. Why would you go with them if there is an alternative? (Having said that, Barcelona is a notable exception; the cabs I was in seemed new and clean and the drivers friendly; not so in Malaga, Madrid or Faro for instance).
Then there is pricing; in a lot of places cabs are slightly cheaper for short distances than Uber, but long distance... I have had quotes of 400 GBP for a cab (and multiple companies) vs < 100 GBP for Uber for long distance.
If they would up their game instead of just whine and long for the olden days, then I would use them instead of Uber, but I cannot see it happen soon.