I'm not a "frequent" negative poster, but I do partake in the negative healer discussions on occasion. I'm gonna give you my personal take, how I have actually felt and acted on forums for years. But it's also one of the most common opinions on negative feedback on video game forums everywhere. So I'm gonna say it in general terms, because I know it's not just me.

People complain because they love the game (or at least, have loved it in the past). And because they love it and play it so much, any sharp edges are very obvious to them. So they complain, hoping that it helps make their favorite game better in the future... As cliche as it is, that's what I believe.

There is a second part to it though. Just enjoying the drama. Misery loves company, and all that. Sometimes it's just nice to hear people complain about something you've been bothered by recently and you just wanna shout "Yes, exactly!"... and then maybe walk it back a little, because damn these people are PISSED, and their criticism is shotgun-style, doing all kinds of collateral damage. Maybe that last part is just me, idk.