Lowering the "front page" $/mile rate could make the service immediately less attractive to workers, who can select between multiple services based on the apps on their phone. Lowering mileage paid is much harder for workers to detect, since it requires carefully checking each trip and measuring what's actually paid.
This could also be an "unintentional-intentional" bug, meaning its presence was just an accident -- but that the company has chosen to prioritize its engineering resources addressing issues that improve its revenue, rather than decreasing it.
In a business that is trying to optimize a marketplace, accurate measurability of everything matters as the performance of every marketplace optimization is degraded by having poor gage repeatability and reproducibility in its measurements. It's like trying to play darts when you're nearsighted and have 20/400 vision. This is process engineering 101 stuff.
There's way more money to be made in having accurate measurements than having inaccurate measurements that optimization engineers can't rely on. The more accurate the measurements, the more confidence you have that your marketplace optimization algorithms are producing the desired marketplace dynamics.
2. I could see a company with various ethical lapses like Uber not prioritizing an unintentional bug for a speedy fix.
3. In the intentional scenario, it'd be a case of https://en.wikipedia.org/wiki/Salami_slicing (popularized by Superman 3 / Office Space). Easier to get away with than a public rate cut, with the downside of bad PR if you get caught.
It's probably a bug that no one will fix or talk about fixing because it makes the company money. Standard large company stuff. You don't get promoted for costing the company money.
This could also be an "unintentional-intentional" bug, meaning its presence was just an accident -- but that the company has chosen to prioritize its engineering resources addressing issues that improve its revenue, rather than decreasing it.