Consider this then: If you could build an app as polished as Uber's, there are hundreds of minicab companies in the UK alone, most of which have apps massively inferior to Uber yet has to compete with them, and that are thus a market for better apps.

There probably is a lot of luck involved in becoming Uber, but if you can make an app that good in a short amount of time, then the opportunity cost in doing that and sending a demo round to a few dozen minicab companies is very, very low.

Yet these companies are still stuck with horrible apps, because in reality it takes a lot of time to develop a good one, even if a prototype is fairly trivial.