Also keep in mind that even at these fee levels, Uber and Lyft are somehow not profitable.

That's really all they (and, to be honest, most "marketplace" tech companies) need to say. They have the customers; here are our terms. It kinda really sucks, because the quality incentive goes out the window.

Technically no, the real-time tracking requires constant data streaming to and from their servers, proportional to the duration of the ride.

But a more likely answer is that a fixed amount per ride makes short rides prohibitive or at least less appealing.

And if you think about it, much of the costs are probably fixed (across all rides), so you could say they should charge $millions to the first ride, then just charge marginal costs for the others. Dilution of costs across purchases is an indispensable part of doing business.