For me, I'd just been burnt out on what seemed like a constantly shifting focus from one half-finished overhaul to the next. Always adding more bugs and tedium, nessecary streamlining and improvements to make it more playable always getting pushed back. From a modder and contributor standpoint you can also see a lot more of how the code is often an untested mess, and you can really see that "broken implementation now, playable version when I get around to it" mentality and how it piles up over the years.
Even with Bright Nights being focused under the direction of the singular most competent dev Cataclysm has ever had, 90% of the to-do list so far consists of fixing broken and badly-implemented shit inherited from DDA. Code-wise it's a train wreck that has been piling up for years, and a lot of the worst aspects of that aren't as visible to players. It only starts to become apparent when you get into modding extensively, and becomes most visible when you try to work with the underlying code as a contributor.
As for the devs having problems...yeah. I'm hardly one to talk, I'm absolutely highly abrasive when it comes to discussing problems with the code, but I'm at least inclined to acknowledge that as a problem and have been trying to avoid getting worked up over things these days. Then I see several of said devs demonstrate that they have not made the slightest effort to improve or even acknowledge their self-destructive tendencies and abusive attitudes over the years.
Hell, on the old fan server, about a week before it got took over by that neo-nazi troll (long, weird story) Kevin in particular had stormed off the server after one of the admins asked him to stop provoking arguments. That was basically the first week I can remember where that server was actually peaceful, and where I could talk about development-related stuff in public chat without getting dragged into an argument. Even with several other core devs who strongly disagree with my opinions on how the project is handled still being there, things went perfectly fine for that one week.