There's a much simpler explanation. At some point, the UI becomes about as good as it can be. It can't really be improved any further without changing the whole

There's a much simpler explanation. At some point, the UI becomes about as good as it can be. It can't really be improved any further without changing the whole paradigm, and just needs to be maintained. But product managers inside the large corporations can't get promoted for merely maintaining the status quo. So they push for "reimagining" projects, like Google's "Material Screw You" UI. And we get a constant treadmill of UI updates that don't really make anything better.