Most of us bitch because we care where the game is going. I'm sure there is a small subset of people who have already quit and given up entirely and are bitching just to be assholes. But I'm also sure that most of the complainers want Yoshi and the devs to keep pushing to be better. We want it to be more fun for everyone. If we didn't care, we wouldn't bother.
Regardless of the bitching, everyone who's still playing the game is playing for their own reasons - in my case, a combination of masochism, blind optimism, and addiction. Flaws, yes, but there definitely are many things I still enjoy about the game and when I find them I do post about it, like the recent Halloween event which was both cute and had some great seasonal rewards. The game itself has a lot of flaws, a ton of things it could be doing better, and as little hope as there is that things will change even after so many patches of SSDD (same shit different day), hope is a very difficult thing to let go of. I have a lot of time invested into this game. I have friends who play, and I do enjoy the content that is fun to play. I desperately want the game to be better than it is, and better than how it's looking like it's going to be for the next few patch cycles at least. I want to log in every day expecting to have fun.
I agree that the complaining and criticism gets to be much too excessive at times, even on BG, and I'm one of the people who bitches the loudest. However, I strongly believe that if we don't complain about what we find wrong with the game, the people in charge of the game will never know what's wrong with it or what needs to be fixed to enhance players' enjoyment. It's a form of feedback. The more people complain about a specific thing, the more likely they will at least see that people are discontent with it, even if they take no steps to fix it. Complaining serves a very important role, and let's be reasonable here: SE has never traditionally accepted feedback in any other form. Even with Yoshi's "new policies" on listening to the community, you will notice there is no "Game feedback & suggestions" subforum on the OF. Even if you want to consider the entire OF as a feedback platform, the lack of that specific subforum is extremely conspicuous for a game whose producer claims he is listening to the community's feedback. Honestly, my own complaints are 20% venting and 80% feedback in hopes that things will change. And I do try not to complain about completely unreasonable things. I'm glad we're getting airship adventures instead of a third dungeon. I would never complain about that.
Unfortunately, it seems then that it's just a big circle: the people who dislike the complaining accepting the game more or less as it is and wishing we would complain less, and the complainers wishing the game was better and complaining more. I know constant criticism is an eyesore for people who find it excessive, but then it shows we value criticism and complaining differently and view it all a bit differently from each other. I am honestly happy for people who can play the game either oblivious to or ignoring its major flaws and don't ever feel the need to rant about it. But I think that is (pretty obviously) the small minority.