The barrier to entry in ride sharing business is so low it's almost non-existent, which makes the whole strategy pointless, unless they can lobby in Congress for some regulatory framework that would make starting a new ride-sharing business harder.
Which would presumably mean they've spent billions to go round and end up exactly where we started? Which is presumably what will happen with a lot of the 'disruptive' companies once public opinion and regulation catches up with them.
I don't know if it's worth as many billions as it's cost so far, but it's not nothing. This is being done because a monopoly of this type is NOT so easily busted by some bright spark 'disruptor'. If nothing else, you can spend a few more billions buying whispering campaigns suggesting that the new 'disruptor' is unsafe or tainted, or simply attack them more directly, terrorize their drivers, whatever.
Even without such black tactics the notion of frictionless liquidity in market dynamics is foolish. It doesn't work that way.
There are user costs to switching platforms, even if the platform is a ride sharing app. I get that the friction is less than something like Facebook, but an amount much, much smaller than 23 billion would have been enough to 1.) have the best app on the market and 2.) advertise/discount where necessary to maintain some market share.
If your customers have an unsustainable business model and you have favorable unit economics and a market leading position, you can quite literally sit on your cash flow (good unit economics and low overhead lets you survive market share losses) and wait until everyone else goes out of business.
Also: you don't need to have "the best app in the market", just a reasonably good one. Advertising cost is more of the issue, but you can do that by starting in one local market, get some market share and use it to attract more VC capital.