He's had an incredibly strong fanbase in Tumblr ever since he became famous practically overnight with Game of Thrones, and his popularity never went downhill. A lot of his fans find him not only hot but also charismatic/charming in interviews which increases his appeal. He's also an overused "face" to use for characters in roleplaying communities, especially when writers put him in gay relationships with characters played by Oscar Isaac for some reason (probably because they're friends irl).
I don't get the appeal whatsoever and find him incredibly oversaturated, but his popularity is very much real and not astroturfed. Thus it'll be a fucking shitshow if they kill off their stronk Latino man thirst-watch representation so pathetically like they did for Joel in the game.