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.
But it's hard for a company to justify "paying to leave shit alone" so even if a maximum was reached, it will recede.