Flat minimal-contrast UI is one of those things that's nearly universally loathed by everyone except UI designers but that has bafflingly persisted in the marketplace for over a decade now. I'm sure there's a nice psychology-study article waiting to be written on the reason for this.

Compare with the equivalent in architecture, https://www.worksinprogress.news/p/do-people-prefer-traditio..., in particular the two photos halfway down where non-architects overwhelmingly preferred the reasonably-pleasant design in the first photo while architects preferred Cell Block D in the second.