I did some research actually. The sticky is now closed, but I posted it there. No good answers. Bascially I wanted to know any game site, any at all that would have that feature. Excluding Steam. And even on Steam, this feature is so hidden, that I used Steam for years and did not even know it was possible.
The fact is, most game sites do not even have tags to begin with.
Maybe it is different for asset stores?
As for the reasons, the single tag exclusion was implemented rapidly after a feature request in community some 5-6 years ago. The fact that it was neither removed, nor implemented or expanded on the site as a documented feature instead of undocumented tells me something.
The calculation of actual usefullness, actual demand, accuracy and such vs. cost of implementing it in current framework is unfavorable. Or in other words, if it were cheap to implement, it would have been done.
Steam has a fixed pool of tags. And they are very accurate because of curators and or popular vote. So tag filtering is not only cheaper for Steam, but more usefull.