You didn't mention which cities you've experienced in the EU, and in any case I've no reason to doubt your experience, but all I can say is that some places with traditional/regulated taxis don't seem to have the same problems. I'm in the UK and I can't remember the last time I had trouble getting a taxi at quite short notice even at a busy time of day, booking in advance is pretty much 100% reliable around here these days, and I've never heard of someone finding they can't get a cab in their area (unless you mean somewhere rural where there isn't a local taxi firm, I suppose).
Edit: in NYC & Orlando I have the same experience by the way; unfriendly cab drivers, no seat belts, crap cars and generally more expensive. But I guess that's not well regulated?
Is there a reason why a black cab driver in London, Manchester or Edinburgh couldn't register as an Uber driver and play for both teams?