I think that there may be something of a sampling bias going on here. The sort of structure analysis of storytelling we do attracts some particularly intelligent and rational people, but also quite a lot who are, charitably speaking, not. It's a constant struggle to keep the prominent pages full of the stuff that's actually worth reading, and to shove the rest under a sofa when we can't get rid of it entirely.

I think it's that the website is dedicated to identifying common structures that make stories entertaining, with an emphasis that they are fictional structures. It's the very use of the word "tropes" in the title. Thus the user base is a bunch of people who enjoy a lot of bad (and usually absurdly bad) t.v., yet also have fun analyzing what psychological manipulation they were supposed to have been subjected to. Also, I know a few TVTropes addicts who are regular LW readers (from a forum on which Dresden Codak left a large impact), and wouldn't be surprised if they have contributed.