It's capitalism and greed enabled by idiot masses, simple as.
They keep making changes because people are stupid and "new" equates with "good".
Most people are too stupid and/or ignorant (mostly both) to understand that AI makes slop.
Even Mozilla hired a CEO it didn't need, to help it do more business? Which didn't happen, instead it turned out to turn off users and lead to a war about the ramifications of giving him money when we found out what he does with the way too much money he was handed. So then they got another one who is equally worthless and wants to AI all the things and also gets paid way too much.
Firefox was really, really good in its early days, when the mission was about being light and fast. But they started ignoring users and also long-standing bugs very early on and the enshittification has proceeded ever since.
Those skinny scroll bars piss me off at least as much as they do you, BTW. You can barely even fucking see them in Edge. In Firefox you can see them OK, but actually using them is a nightmare. The easy fix only works on Windows, too, you have to manually edit config files on Linux. It's hard to not see that as an attack on Linux.