I honestly can't fault Microsoft alone per se for this, TBH. It's just, as someone said, the modern web.

The highest KB bloaty JS I see is the Youtube embedded video player (about 500K of JS and CSS). There's also a bloaty 200-300K "sprite sheet" gifs, which per the code I guess they are using as some sort of video. (I wonder if that could be optimized.)

There's a lot of the usual tracking and analytic scripts, of course. Microsoft has their own in this (Application Insights) but of course you've got the Google and FB and other standard social media scripts.