Pullman said:Because people prefer looking outwards, not inwards. What I mean is that they're more comfortable judging and labeling something outside of them (in this case the anime) instead of focusing on themselves (in this case their experience/perception of the anime). They like to pretend they have nothing to do with the watching experience and whatever the result is, is all solely because of the outside object, the anime.
It's psychologically much more relieving to put all the blame and responability outside of them and see themselves just as passive mediums who mechanically react to what they watch as if that was the only possible reaction. Or the only 'logical' reaction at least. Which is why they can get so passionate (read: insulting) when someone else doesn't share their perception.
It reminds them that it's all subjective and that their own expectations, knowledge, history, current state of mind, surroundings, values and preferences play at least as big of a role in how they perceive an anime than the anime itself. The anime itself is not a variable, it's always the same no matter who watches it. What changes are all the personal variables I just listed (and many more probably). And to some degree we can control them if we are aware of it, shaping our experiences into something more enjoyable than it would have been if we just pretended to be passive mediums.
But all of that is a somewhat complicated concept and it's super annoying because constantly being aware of it makes it very hard to form quick judgments or opinions about pretty much anything, which is something human psychology yearns for. And the introspective nature of that concept forces them to reflect on themselves more than anything, if they take it to heart, which is something most people do not enjoy at all.
So they stick with the quick and easy shortcut of calling shows bad or good and whatnot. Everyone aware of how truly subjective perception is by nature will know that they're still only talking about their experience/perception of the show but to the masses it's all the same. And functionally it is too, to some degree, when it's just about making your opinion heard. But it does breed countless conflicts and misunderstandings that could be avoided if people were aware that all perception is already colored by default through the glasses of their individuality rather than thinking that they 'perceive the show as it is'.