If anyone is wondering about the user studies that Microsoft did for Windows 95, you can read about it here: https://web.archive.org/web/20060615110538/http://www.acm.or...
Windows 95 is under-appreciated in the GUI histories I feel - it had many things that became 'standard' pretty much immediately afterwards (I even have a shortcut to Applications in my Dock which mimics a Start Menu).
But it's hard for a company to justify "paying to leave shit alone" so even if a maximum was reached, it will recede.
I agree. There's a lot of people paid to re-design Windows every year, they all use Macs, and none of them are doing any user studies at all.
I suspect user studies are being done - and coincidentally confirming whatever it is management wants to do.
Or they focus on new users and not on the amount of things people have already learned.
They've spend the last few decades undoing all that work piece by piece until nobody actually knows how to use it anymore.