The problem, I think, is that while you named an example of being (maybe) "over-invested" in a manga, SPN fandom is over-invested in their fake canon that will never come true and is full of problems, but OMG IT WOULD BE REVOLUTIONARY SJ TV... which is where the cognitive dissonance and "HOW ABOUT NO" sets in, wank-wise.

Given what I've heard about SPN it wasn't that revolutionarly SJ to begin with. Mainly white dudes with a side order of white chicks, and not the best treatment of the white chicks narratively speaking. Sleepy Hollow beats that record and we're only five episodes in.

I may be wrong, I've never watched it.