This is not a question because I exactly know how to do that.
I mean, I have 2 specs and therefore 2 sets. If I switch between talents I have to dress up everything manually. I tried to write a macro to click button 1 and 2 (mouse) but it’s limited to 255 characters.
So the question is why do we have to do it in so uncomfortable way? We have 2022 year and a lot of experience how to fit the UI to our needs.
It was done this way back in original WotLK as well.
My personal guess is since most people already use some form of equipment manager (Itemrack, Outfitter, Wardrobe etc), they would probably cause problems for many people, so easiest solution was to leave it disabled as default.