That's one problem. I typically need a taxi when I'm in a remote city a long way form home. Uber gives me a common app that works from Sydney to San Francisco. I'm not going to land in Chicago and work out which of the myriad of apps I need to get.
Now if it was instead a website, sure, much easier. No need to create accounts etc, just visit "chicagotaxi.com", perhaps shown on a sign at the airport/station/etc, then book and pay with applepay/googlepay.
But installing some application, signing up, having my data stolen, all to be told "no taxis available", is the reality of a local app.