Uber/Lyft could allocate the "new car in" slots using whatever mechanism they currently use to match riders to drivers.
Having to find "my" car is just completely backwards in the airport scenario, at least at times of high usage.
What is that reason, and why are things handled so differently for taxis?
In most cases it's a simple capacity problem. Taxis have to be hailed physically, and there are already reserved taxi stands at every airport. There's no reason for that to change.
A more efficient stable state is clearly not being reached through market forces, but since there will never be agreement on whether that's due to too little (get rid of the medallions!) or too much market liberalization (ban the rideshares!!), and the only thing everybody can agree on is that a public transit solution is impossible, I don't see any way out.
> I'd be willing to pay extra to just get whatever car is right there
So then just go to the taxi stand? Why even call an Uber?