I took an Uber from Taipei City to TPE airport. I was charged for the a "return fee" to account for the inconvenience of such an out-of-the way trip.

It was still dirt-cheap compared to a equivalent trip in the US.

Why not? It's definitely sustainable. The loss can be offset by the gains. And if the gains outweigh the loss then it's sustainable.

It's sustainable - if prices for regular rides rise to compensate for the losses drivers take on less profitable ones.

... and all of a sudden, you are back to taxi pricing.