It's not too complex to implement. Think of uber's USP a taxi in X minutes ,the smaller the X the more rides they get.

Analogizing to the past ,let's say you hailed a cab before Uber and had to choose how much the driver would charge, would you do that?

A metric based pricing (distance with some initial price) is much more time efficient for the rider and driver.

I know that travelling X miles will cost y $ across the board. If I have to not only choose type of service but quality of service that's one more thing I have to do. Given that we know I will pay close to $Y for X travelled any cost plus price around Y seems logical to me.

Issue with tech coming into play is the cost X is significantly decreasing ( threatened by reducing driver pay)

If we take into account driver pay as a separate part of cost per ride, then eliminating that makes most sense.