One reason is that a good part of their claimed novelty is being able to hail a cab via mobile-phone app (as well as get pricing and such), which is not actually novel in many markets. In much of Europe the existing taxi companies have that feature and it works just fine; it's not too hard to add it as an incremental improvement to the traditional radio taxi. I used the app from 'AAA Taxi' a bunch in Prague last week, and I don't see what Uber would offer above the existing functionality.