I've been told by a friend who works for Uber in their p.r. department that it is for the various outages they've had. The bonus amount is based on the length of the outrage in each city adjusted by the city's average earnings per driver. And no, Uber did not suddenly grow integrity. They been losing drivers to Lyft at a significant rate, so they've now changed tactics and decided to be more "driver friendly' for the foreseeable future.