Sam and Dean have long been the odd boys out on the CW's roster. The average scripted drama on the network is about a group of attractive young people dealing with either high society (Carrie Diaries, Gossip Girl), the paranormal (Secret Circle, Vampire Diaries) or both (Reign). These shows are aspirational in the way young adult novels are. Supernatural, by contrast, comes from a distinctly older form, mashing up the X-Files with Starsky and Hutch. Leave the CW on for any length of time and the Winchester brothers, Castiel or any of Supernatural's other characters will look old by comparison.
How does such a show keep up, and stay on the air, on such a youth-oriented network? As the show hit its stride around 2007-2011 producers Eric Kripke and Sara Gamble developed and excelled at a distinctive strategy. Instead of portraying characters that the CW's fan base might wish to be, the show portrayed and interacted with its fans as they were. The introduction of "Supernatural," a series of YA novels inside the fictional world, and it's attendant fan culture, meant an opportunity to meet and foster young engaged viewers on their home turf of fan work and social networking. Discussion of fan fiction isn't revolutionary on television in the last ten years; it has been fodder for a number of procedurals. A scripted show discussing its own fan fiction and name-checking prominent internet fans in the canon was not only novel, but also catnip to the young audiences who naturally interact with their shows through fan labor and online community. As the show progressed, fans began to be directly portrayed in the person of Becky a (loving?) parody of a representative fan, as well as numerous others involved in activities like con attendance, cosplay and LARPing. When the phenomenon of 'two screen viewing' became the norm for the CW's target audience, Supernatural kept up, with characters (notably actor Mischa Collins momentarily playing himself) tweeting from inside the fictional world into that of the fans. Beyond the novelty, this dialogue with its young, involved fans has cemented Supernatural’s place with its extremely loyal audience.