"Why do they make these changes? Who asked for different right-click menus and toolbars?"
It's the same as the reason behind Windows "Ape" and Win-10-nic. CHANGE for the SAKE of CHANGE!
A bunch of millenial CHILDREN noticed that a whole bunch of us old farts have either retired, or moved on to other things. As a result THEY were left in positions of reasonably high authority. A handful of 'old farts' remained behind, but were easily tricked into believing whatever CRAP the millenials were preaching.
After all, to these millenials, it's THEIR turn now. We old farts are DINOSAURS, sticks in the mud, living in the past, refusing to change, refusing to adapt, refusing to believe that what THEY want to do is so superior to the way things have been done for DECADES.
It's THEIR turn now, and DAMMIT, they're gonna SHOVE IT
UP OUR DOWN OUR THROATS, for our OWN GOOD, whether we WANT it or NOT, because, CHANGE is *ALWAYS* better, right? [in THEIR minds it is apparently so]
In the case of Micro-shaft, they went to "the Metro" UWP and a phone OS on the desktop. Unity isn't much better, but THANKFULLY it was ABANDONED by Canonical.
However, Canonical still needs a CLUE BAT when it comes to systemd and Wayland. And so do the project managers over at Debian [hence, Devuan].
Obviously these people have NEVER read Arthur C. Clarke's 'SUPERIORITY'.
So that handful of "old farts" who STILL retain some decisionmaking power should *NEVAR* enable those damned millenial CHILDREN who want all of that "change for the sake of change". Just because they're YOUNG does _NOT_ make them "hip with the latest beat". OK my age is _REALLY_ showing now.
The fact is, THESE CHILDREN do _NOT_ know arses from holes in the ground, CRAP from shinola, etc.. They *FEEL* they do, and their emotions drive them too much. "Old Farts" that ENABLE them are as much to blame, if not MORE. Yeah, it's HARD for some people to say "No". I had to teach that to someone a long time ago who fell for telephone hard-sales too easily. You just say NO, and hang up the damn phone. "What do you say when they start talking about how you need this?" "NO!"
Same with those 2D FLATSO 4" phone UI loving millenials (some call them "4 inchers" based on how they see the universe through a 4 inch screen). They have NO CLUE what's possible, and they're more than willing to TAKE IT AWAY and SHOVE THEIR CHANGE into whatever bodily orifice an unsuspecting end-user might have, simply because they are:
c) full of themselves
d) horribly misinformed
e) short sighted
g) living in a bubble world of ONLY others like themselves
h) totally clueless
i) unable to drop their phones for 5 minutes and have a REAL conversation
j) way too influenced by social media
k) caught in the trap of "new, shiny"
and that's all about I can think of at the moment. Add all of that up, and you get your explanation.