Ride-sharing apps are just apps, and the barrier for adopting a new one is low, for both sides of the market.

It's easy for two people to start using a new social network as well. That doesn't mean they'll want to do it if they're the only two people on it.

More Uber users -> larger market for Uber drivers -> more Uber drivers -> higher availability of drivers for Uber users -> more Uber users -> etc etc

Further, Uber’s political operations benefit the other apps equally.

They could push for monopolies at the municipal level, much like cable companies do.