Earlier quoted context omitted.
The hard part of Uber isn't the tech, it's building up the network. Two-sided marketplaces are really hard to build from scratch, when there are no competitors. They're virtually impossible once both your customers and your drivers are like "I've already had good experiences with Uber. Why would I take a chance on you?" That's why Google has an advantage over everyone else - for them it's a one -sided marketplace, th…
The answer to "Why would I take a chance on you?" is simple: "I'm cheaper." Neither Uber's passengers nor their drivers are deeply loyal. They are for the most part brought to the service by the value prop. Uber is of course an established brand, and that brand has some value, but the value is hardly infinite. A deep pocketed competitor could establish themselves.
This sort of cross-subsidy has a poor track record when used against well-capitalized opponents. (In many situations, it's also illegal: see "dumping".) Unless you can complete wipe out the competition and force them out of business, you're pouring money down the drain, and building nothing of value with it. Bing Cashback resulted in most people doing their searching on Google, identifying what they wanted to buy, and then buying it on Bing so that Microsoft would pay them.
You get very odd arbitrage situations that basically result in funneling money straight from the corporation that's being idiotic to a savvy consumer. If a company did what you suggest, I would immediately sign up with them, along with my fiancee. We would then use the app every time we took a trip together or picked each other up. Since one of us is the driver and one is the passenger and the driver earns more than the passenger pays, we'd be making money at this company's expense every time we drove somewhere. Now imagine every carpool, group of friends, or just random strangers who setup a business to exploit this arbitrage opportunity doing that.