My hypothesis is that they try to figure out what prices to set to extract maximum profit, based on how much they think you're willing to pay, how busy the driv

My hypothesis is that they try to figure out what prices to set to extract maximum profit, based on how much they think you're willing to pay, how busy the drivers are, how much profit they're currently making in that geographic area, etc. It's much easier to entice new riders by giving them coupons than it is to generally lower their fares.