This was justified with, "I am an HCI expert, trust me". Which is garbage: I'm the user of the tool; don't try to pretend you know better, like some colonial governor.
Also, it started getting slower. A process that only got worse and worse.
My assumption is that it was really all driven by internal politics within Microsoft, specifically some manager's need to Change Something.
Strongly agreed. Better for newbies, maybe, but disastrous for skilled users. It broke the suite for me: I can't stand it at all, and switched to LibreOffice full time.
Sadly, though, LO Writer doesn't have Outline Mode, the one indispensible bit of MS Office for me. So I keep Word 97 or Word 2000 around, just for outlining.
The whole ribbon interface debacle looks like a classic case of enshittification, where the users are no longer the customers anymore.
But Office 2011 is 32-bit and no longer runs. Now, I only keep Word around. I've been forced to update to 2016, the oldest 64-bit version that'll run on macOS 11 (AIUI).
The menu bar is an inextricable part of the macOS UI so it would be hard to remove, but it demonstrates perfectly that Office for Windows could have kept both UIs, because the macOS version did.
My normal mode of operation in Word for Windows uo to 2003 is just to turn off all the toolbars, and the horizontal scrollbar, and the ruler. It runs well with nothing but a menu bar and every feature is usable.
Indeed - I remember this situation very clearly. Back when Office 2007 came out, there was no first-party way to create applications like that, and after a year or two, only few third-party libraries that were lacking in quality and polish.
This was the turning point. Clients asked us for it, we tried, but ultimately we decided to ditch the bad libraries and do our own thing - then the clients decided they might as well define their own UI design language if they're paying for UI component development.