I try very hard to understand why they do some things, and come up short. With a lot of the minor UI tweaks, it's certainly not based on any real-world research, because some of the tweaks go against what's already established or being published in journals.

They probably do have reasons, but as to what they are, no idea. And as to whether their reasons are beneficial to the user, in many cases I can say no, absolutely not.

They've recently screwed up enough things badly enough to severely abrogate user trust, and I don't think they even realize it.