I think it just happens. Until around 2 years ago I was essentially a guild-hopper. Not on purpose, mind. Most of the time, my guilds disbanded or fell apart and I ended up having to find a new one since my primary focus in the game was (and is) raiding. I've played WoW for around 10 years, but only in the past 2 years have I found a guild I think I've actually settled into with no plans to leave. It's an old guild and it has gone through some rough times, but it sticks around and survives and I really like the people in it. They're odd, they're quirky, they're my friends. They downright piss me off sometimes, but I like them and I'll stick with them. I like everyone in my guild, precisely because most of them are total weirdos and that suits me because I'm a weirdo too. It's perfect.
It's not a hardcore guild, we raid Mythic 3 days a week but we're not bleeding edge (currently working on Gorefiend). I'm okay with that. I like progressing on Mythic but I don't expect us to blast the rankings (especially on our server) or be godly, as long we get there slowly but surely. It's nice because it's a guild that allows me to focus on improving my own play all the time with only a little pressure, but it's not stagnant. We have a shouty raid leader who is actually a very nice person, he just shouts at us all the time in raids and I guess you have to be used to it, haha. It doesn't bother me. If anything it's probably necessary because we have a pretty wide skill spectrum here and some of us need to be yelled at to play properly.
It took me a long time to find a guild I knew I'd stick with, I figured I'd be a guild hopper until I stopped playing. Even now I'm amazed I've stayed in one guild for 2 years now. Usually I was lucky if the guild I joined lasted 6 months. Even if this one collapsed I'd stay, I feel like they are my friends and I would want to stay and help rebuild or go somewhere else with them than go to a brand new guild. I feel too old to go making applications to join a brand new guild full of people I don't know, haha. Maybe it's because I've had to do that so many times in the past and now I'm tired of it and I don't want to do it ever again.
The main factor in finding a guild you really want to stick with is clicking with the people in it. That guild also has to share your goals in-game to a reasonable degree. If you've got both of those boxes ticked and there are no major problems in the guild (politically, roster-wise, etc) you will likely have a guild you can stay with. Outside of raids I chat with people and play other games with them and I can call them my friends. My raid leader may be yelling at me and others during raids, but outside of raids we'll shoot the shit and have a laugh doing other things.
I guess the social side of things is the main factor. If you're in a guild where nobody talks to each other and you only log in for raids and then log off again... well, those guilds don't tend to last. I've been in guilds like that and they have always without fail disbanded. There was this air of "I'm only here because I want loot, I don't like any of you people" and that does affect raids negatively. For me, it takes away most of the fun of raiding. It's a social activity and it should be fun and we should all feel like a team and enjoy playing together, even if and when one of us fucks up.
This got long. I'm just a bit bored and rambly right now.