People love saying "everyone else has this feature already and it works great!" when it's not remotely true. Wouldn't be the first time. They tried to complain the same way about payouts, back when itch.io had the shortest turnaround out of all the major websites where you could sell stuff. It's almost as if truth was an inconvenience.
Oh, there are content sites with exclusion of tags, but specific to gaming it seems rare, except for the market leader. One would think that many would imitate Steam for that, but apparantly not.
Might have to do with the catalogue size. Of the other sites, Steam has the biggest by far, yet they only have ~160k titles compared to the ~850k titles on itch (560k claim released status). And of course, the other sites usually lack the tags to begin with.
I believe Steam just added it, because it was dirt cheap to add into their existing framwork of tagging. It starts with them having only a limited selection of tags and when filtering their catalogue by tags it appears as "tag" and "-tag", so basically, even the exclusion tags are positive searches.
In contrast to "filtering" on itch, that is done (or appears) as added sub urls. My guess is, that there is not really filtering done at all. It is a cross-section of overlapping url conditions. And there just aren't nightly builds of negative tags that could be overlapped. There would have to be built two lists for every tag, and since tags are custom, one does not just build a list of 1-million-minus-the-seven-games-with-obscure-tag to overlap ... for every obscure tag.
So starting at my guess, filtering would not be integrateable into existing browse, but would have to be added on top. For singular that was trivial. For multiple, it apparantly is not.
But it might be a help to many, if the existing option would be available as an UI element in browse. I would not need it, but that is because I do not put too much weight on tags anyways. Dev tagging is often horrible. Tags on Steam are user chosen by majority. At least it says "Popular user-defined tags for this product" under a game.
as you said, it's as if the truth was an inconvenience...
I mean as the other guy said, itchio needs this because it is a problem here on itchio, not because it's just a simple "Quality of Life improvement", I see lots of other (dare I say, unnecessary) updates but this problem has never been solved, I doubt the Devs are even taking this problem seriously. I don't know what happened back then, but I'm pretty sure it's a much-needed improvement here...
It's been frustrating for me too, not knowing what to tell people for such a long time, but I trust the dev team. If they weren't able to do it in years, there must be a good reason. Edit: in all this time, people continue to demand and assume bad faith, which is doubly frustrating. There are many other features on itch.io that can help us discover games, but people won't use them because they've decided that the one thing they want is tag exclusion and nothing else.
If people assume bad faith, they should apply Hanlon's razor. Also, if I were to believe the threads about tagging and exclusion, I would also have to assume horror is unpopular. Well, horror is very popular on itch, so maybe tag exclusion is not in such a high demand, as those threads might suggest. After all, the people happy with recommendations and related games and other means of finding games do not regularly make community threads about how things are ok. It is the people fed up with horror stuff that do.
Sure, it might be a handy feature in some situations. But would it be a feature that most users would use? Or is this one of those scenarious, where the people able to use that feature would not need it, cause they would know how to find stuff without it.
I have trouble believing someone looking for the 10k new games in the last month. Like, itch show me everything, except horror and visual novels, I will dig through the remaining 8k games myself. To be realistic, you have to start somehow with positive filtering. And this should thin out the games already. And who knows, maybe that puzzle platformer pixel adventure you might like, does has some minor horror elements that made the dev chose horror tag - after all, horror is popular, so everyone and their dog is tagging it.