I think it may be less unconscionable arrogance (@VJCatmur) and more unconscionable indifference, fueled by management's top-down push to make their platforms and interfaces more cloud-friendly and Apple-like. The people making these decisions are rarely technically adept but instead are money/business-people. Modern Comments, Modern OneNote, etc., reflect a deprecation of power-users and an increasing emphasis on market-strategies that pander to populist mind-set and abilities. I claim that the typical Office user today is relatively unsophisticated compared to the typical Office user of years back, and we power-users are in a dwindling minority (1). Bucks drive corporate decisions.
Having said that, there are some clear advantages of Modern Comments over Classic Comments, and vice versa. IF they can blend the best of both, it will be a winner.
Modern Comments Likes : Modern Comments in dark Focus Mode is superior graphically (as a writer, this is not merely cosmetic); comment-thread tracking is better, etc.
Modern Comments Dislikes : unlike Classic, when in Modern mode about half of my comments warn "This comment contains content that's not yet supported" (tables, graphics, etc.); Modern is a keyboard-shortcut wasteland compared to Classic; hyperlink-handling is significantly worse (e.g. hashtag/bookmarked hyperlinks don't work!); Rich Formatting is largely gone and Modern has reverted to barely above plain text circa 1990/2022; and for the love of Zeus why do I have to click a button to edit my own note?
(1) How many of us power users (intermediate to advanced) are there? Well, back of napkin, if there are https://www.bing.com/search?q=how+many+people+use+microsoft+office and half of those use Word and 10% of those are intermediate-to-advanced (savvy enough to bemoan Modern Comments) then that is 50,000,000 (fifty million). Let's be cautious (dystopian?) and suppose it is actually only 1% (one out of one-hundred users are intermediate+ Word users), then that leaves five million of we happy few across the planet.