Traxy of I Like Pancakes has a great article up on the foibles, let us say, that a tank faces in a random LFD pug. Beruthiel of Falling Leaves and Wings has a similar article up, but that one describing the downright abuse that tanks often get, despite doing everything right. Beruthiel's post gives a strong suggestion about why tanks are scarce in the LFD tool.
I have tanked a few LFD runs, and I see a lot of what Traxy and Beruthiel describe. I've been flamed for using resilience to get uncrittable (when that worked), and I've been flamed for taking the Pit of Saron gauntlet in three pulls instead of two. It's usually something where there's a common way to do things, and then another way that is sometimes better but that isn't as well known to the player base.
On the flip side, I keep coming back for more. A lot of the fun of Warcraft is that it's multi-player. If you can let the jerks just go their way, you meet a lot of other people who make it fun.
If you feel the same way, you'll love Pugging Pally. It posted the above two articles as guest articles, and it has a steady stream of posts that "look on the light side of LFG".