The oddity for me is why, given all the RPGs in the world that people don't play, so many non-4e players felt (and still seem to feel) compelled to explain not only that they don't play, but why they don't play, and why those who do play are making some sort of suboptimal aesthetic judgement (eg sacrificing "simulation" for "gamism").
Because it wasn't just another RPG, it was
D&D.
Throughout the history of D&D, as new editions have come out, the general consensus of the D&D player base has been, over time, to migrate to the new edition.
OD&D gave way to AD&D, which gave way to AD&D 2e, which gave way to D&D 3e, which gave way to D&D 3.5. Yeah, you'd get some holdouts to older editions, but the substantial majority switched over without a lot of fuss. Some sooner, some later, but most all of them in time.
In the pre-release marketing materials for 4e, WotC not only acknowledged this, they admitted were COUNTING on it, they pretty much assumed that no matter how they changed D&D, the broad consensus of the D&D player base would adopt it over time because it was D&D. The metaphor they used was to a long-running rock band that put out an album with a really different sound, that the fans of the band would still buy the new album and listen to it. The problem with that metaphor that WotC built 4e on was that that a music album is maybe $15, and is mostly a passive experience of listening, while a new D&D edition is hundreds (or thousands) of dollars worth of buy-in over years, and hundreds of hours of interactive gaming over those years.
4e was such a radical shift, that while it held the name D&D, it didn't look, feel or play the same to many/most players. Whereas previous editions built incrementally on each other (1e to 2e, 3e to 3.5e) or at least tried to retain much of the overall feel even if the mechanics changed (2e to 3e), 4e wasn't an incremental change and it didn't try to retain any of the prior feel of D&D, instead being a completely unrelated game with the "Dungeons and Dragons" name attached. Even if the game was well balanced, well written, and could be enjoyable to play, the divergence in play style as well as the complete jettisoning of around 3 decades of accumulated D&D meta-setting like the Great Wheel meant that if not for the "D&D" name on it, you wouldn't even think it was the same game.
The cultural presumption of adopting the new edition was shattered. If you look back at old threads from circa 2008 the 4e adopters were befuddled as to why people weren't switching over and wanted explanations as to why they wouldn't automatically adopt the new edition of D&D (a lot of early Edition War threads really did start with 4e adopters questioning why 3e players weren't switching, like the automatic presumption was that all D&D players would move over).
That's why people explain it, because when the Edition Wars broke out, it was largely over the presumption that the new edition of D&D replaces the old one, and people move over to the new edition, and that position has framed the view of 4e for a lot of people since then. Adherents to 3.x D&D who reject the radical changes that came with 4e felt both spurned by the process, and excluded from D&D by the changes to the game they love taking a direction away.
There you go, a lot of the root of the edition wars and why they are framed as more than just a dislike of one RPG over another.