There's a certain tension in those pairings that just hooks you, isn't there? It's rarely the fluffy, easy romance. You've got the 'golden boy' type character, the one the story initially frames as the hero or the chosen one, and then you have Yuri—often brooding, morally grey, or carrying some deep-seated trauma. Readers aren't just there for the kisses; they're there for the clash of ideologies, the forced proximity, the enemies-to-lovers slow burn that takes a hundred thousand words to resolve.
I think it also taps into a desire to explore the darker or more complex corners of a fandom's world through a relationship. The straight-laced MC often has to confront realities they'd rather ignore, and Yuri drags them into it. It's not about fixing the 'broken' one, but about mutual, sometimes destructive, change. The appeal lies in watching two fundamentally different people find a twisted, specific kind of understanding that the original narrative wouldn't allow.
Plus, let's be honest, fanfic writers just excel at writing that angsty, possessive, emotionally charged dynamic in a way mainstream media often shies away from. They'll dedicate 50k words just to the 'I hate you but I need you' phase, and a dedicated audience will devour every update.