I expect current UI trends are informed by focus group testing that starts with the application in a blank state and adds small amounts of data. You’d get very different results if the focus groups concentrated on using the application in a mature state with ~months worth of data in it.

My hypothesis is that UI designers optimize towards "pretty" at the detriment of functional because pretty is much easier to show with a screenshot in a portfolio or on Twitter.

The decisions are made based on shared telemetry which many power users turn off. I keep my deliberately on for this exact reason.

I keep it on as well - just hope that they can see that after 89.0 was releases there was an increase (not big, but still) in changes to default look'n'feel and make some conclusions :)