I think there are "classes" of features people have disliked. Eg: every social media app added "stories" at some point, using up screen real estate. Same goes with "shorts/reels/etc".
It's one thing when a feature gets added to an app.
It's another thing when it happens in a context where every app is doing it (or something similar), and you see it in every facet of your tech life.
In this case, Calibre does not seem to introduce any said annoyances (probably because it is FOSS, so no pressure for adoption), but people are upset anyways.
There are many features I don't use in various software, but it never made me complain that a new icon/menu entry appeared.