I think the associated "mythos" and all the online communities they create is a big part of the appeal of these shows. Scouring every scene and interview for clues, predicting what will happen well in advance, etc. Because they take forever to answer the big questions, tons of different theories can exist at the same time and everyone can feel like they're right (until they're eventually not, another reason why people often hate the endings of these shows).

they are so obssesed it spilled over being a parasocial relationship, when the actors started doings cons for the fans, it just got awkward and wierd, if you heard about the death threats agains the actors(the mother and child that was with dean in first few episode of season 6, they couldnt return because of that) the fans got it in thier head they were ruining the relationships, that the characthers were gay. the more cons they did the more bizarre the questions were, plus i think thats why mark sheppard(crowley) stopped doing them.