Well but does that matter as long as mods aren't considered canon?
Quite a bit actually.
For example, to talk about a different game, its often tossed around that modding was one of the reasons the dev of Free Cities disappeared. The mods for the game involved a whole bunch of stuff that was, legally, in a pretty rough spot in some countries (including wherever the Free Cities dev was), and they got really popular, which meant that that stuff was associated directly with him. He asked at one point for the cessation of it, but of course it didn't happen. And now freecitiesdev is gone (though they disappeared without explanation or any contact).
CoC1 kinda got put in a similar position. The game was distributed all over the place, and there was no real way to control it, so in a bunch of places the game with a bunch of stuff the devs didn't really want to be associated with was being linked directly to them. On top of that, people would submit bug reports and message the devs pertaining to modded versions of the game, which were of course a waste of everyone's time.
It's also compounded by the idea that there's an official way to get your content directly into the game, so modding could be seen a bit less necessary than other titles. Doesn't affect gameplay mods ofc.
It was apparently overall just a huge hassle, and with them wanting to monetize future games on platforms outside their website, they decided to just ban mods on the forum in the future.