They don't have to be "evil". They have incentive to want to spend less on compute, but also to not let people know that they are reducing the compute per call.

Like any for-profit: lower loss / higher gain?

Keep competitors in the dark, keep money flowing in, dismiss all the complaints and lawsuits that could come from their changes, dominate the ongoing discussions about AI regulation (if outsiders can't even tell whether the model is changing or not, who would listen to them?).