What do you consider "monopoly profits?" As of the 2013 leak, Uber was grossing $1bn in revenue [1]. Uber takes a 20% cut from each transaction, and has an extremely lean cost structure - drivers pay for gas, insurance, amortize vehicles, don't get any benefits, etc. Even if we assume costs to be 10% of revenue (which they aren't), Uber still would have earned a gross profit of $100m in 2013. Judging by Uber's current $50bn valuation, their revenues have grown anywhere from 3x-5x over the past 2 years. [2]

So by my rough estimations they're making $300-$500m in yearly profit (hardly loss-leadership), and they still haven't driven Lyft or conventional cabs out of service. This is also without taking geographical expansion into consideration. Uber is sitting on a goldmine of a market that it has barely begun to tap.

So what if Uber does manage to establish itself as a monopoly? Then we look to the price elasticity of demand for Uber's service, which measures change in demand over change in price, aka how bad people actually need the service. Cabs are essential to a large group of people (businessmen, tourists, blind, etc.) and in high demand for almost anyone else that lives in a large city such as NY or SF, where it is uncommon to own a car and often inconvenient to take the metro. Therefore they will have a large bandwidth in which to raise their prices in large cities before users start to disengage with the service, opting instead to walk or take the metro. Smaller towns, where people don't use cabs as much, do not present a large market for Uber, but it costs them next to nothing to get users and drivers to download the app, therefore there are no prohibitive costs of investment stopping them from expanding operations other than a natural lack of demand.

If they jack prices up too high for an extended period of time in the cities, another company will enter the market and pick up the churned customers, much as Uber did in the broken, monopolistic taxi market.

So ultimately they will be able to make a very healthy profit, and will not need to worry too much - unless the government decides to intervene with some serious anti-trust legislation, but it probably won't as long as Uber is paying a cut to the cities that it operates out of.

You are right that there are low barriers to entry in this market - it's why most drivers do both Uber and Lyft. The underlying technology is the same, and the capital (drivers) is not proprietary and can be shared between different companies. However, if Uber were to stipulate that drivers sign an employment contract, and then enforce that they were not working for the competition, this would raise the barriers to entry for competitors. Likewise, there isn't much differentiation in the taxi market. It's nice if a driver comes with water and a nice-smelling car, but ultimately it's not a deal breaker.

Ultimately, the network effect is key. Get the most users on your service, get the most drivers driving for you, beat the competition, then erect barriers to entry around your castle. Just don't piss the peasants off too much, or they might try and revolt :)

[1] http://techcrunch.com/2013/12/04/leaked-uber-numbers-which-w...

[2] http://www.forbes.com/sites/chrismyers/2015/05/13/decoding-u...