Red and green

Blue and orange

DECEMBER IS TOMMORROW.

Misogyny, because they struggled to write a good female character. With that in mind, they wrote male characters with a lot more complexity than female characters. Cas and Dean were inevitable. Whether it would be them specifically or two other male characters, it's irrelevant. Jensen and Misha had insane chemistry. Misha himself poured a lot of passion into Castiel as a character to the point where he became a staple of the show, even though the writers didn't always like it. The characters themselves really lend to them having queer and romantic overtones. And homophobia came in too. This show, as the network wanted it, was meant to be about manly adventures, male woes of heroism and loneliness and American values. They didn’t like the fact thar the story wanted to go somewhere else, wanted to remain profitable and marketable to as many audiences and countries as possible and so they could never "sully" their perfect macho American show with two, ultimately soft, queer dudes (and I use dude liberally for Cas because the character has an interesting potential for gender discourse).

But it's ultimately misogyny because none of the female love interests had any substance. None of the female friends were written with character and integrity enough to see them as actual people so what's there to ship? A pretty object with no substance? Someone you find aesthetically attractive but who comes with family, kids, normalcy, a job - things Dean in particular could never have? Someone he can't be himself around? Someone who would nag him? Worse. The other alternative is that they could have written a suitable female hunter. But they didn't because they wanted to write the whole "I'm so lonely, it's so hard being the only person stopping the end of the world, all I got is my brother (who begrudgingly accepted his fate)" type of narrative. Which is rooted in patriarchal views of men being the only capable being. Which also intersects with the individualistic culture we see in Western countries, especially in the US.