I don't think it is? most drivers I've asked have used both uber and lyft and would switch for special incentives; I know a lot of passengers who only use lyft because of the bad reputation uber has, but of the uber riders, most of them also have lyft, and switch based on incentives.
I mean, you need a critical mass in a short period of time within an area, but that's just a matter of throwing money at the problem, and there's no reason you couldn't be a perfectly reasonable regional player in this game.
I mean, of course, at current prices, where margins are all but negative, that requires a lot of money; but in an environment where uber charged enough to have a healthy, profitable business? whenever the uber margins started to climb, you'd see regional competitors popping up.
I mean, that's just my guess. We don't know, because we haven't seen a high margin ride sharing pricing scheme, not after uber made it clear that companies didn't need to follow taxi regulations.