I very very rarely unwatch people. I will always unwatch someone if they aren't the person I thought they were, usually. Like if they seem like a nice person at first, but they actually are far from it, regardless of how much I like their art. I'll also unwatch if they've been inactive for a while.
very rarely I'll unwatch someone I watched a long time ago, and they haven't really improved much/at all, and I've lost interest. That happens very rarely though
When I find myself deleting their activity without even looking at it. Or when they totally spam about useless things like "Lel just go home from the grocery store!" or "Just took my dog for a walk!" It just makes me super annoyed like this is DeviantArt not Facebook
I don't unwatch a lot, mostly banned/deleted account (not even inactive unless I'm following them somewhere else) and people who irks me (being mean to others/annoyingracist/homophobic/hypocrites, creating drama, etc)
I'm very picky when it comes to the people I watch. If I can't learn anything from their art, then I don't follow them. And/or their art is not what I want in a style anymore. I only obligate myself to watch/follow people who are my friends.
Either within a journal(s), deviation(s), or poll(s), they have offended me. Not in to case that I simply don't agree with views, more of they're believe prejudice thoughts and values. As an absolute equalist, I simply must not watch and/or support those with views of discrimination of any kind, to race, sex, sexual orientation, political standards, or interest. It's not about hate; it's about humanity, kindness, and acceptance.
I usually only unwatch if all they do is post a bunch of drama That and I went through my watch list a week or so ago and unwatched everyone who I didn't immediately recognize, since I was watching over 500 people and my inbox was way too full