>>3054340They have an interesting dynamic and they're both fairly complex characters who are situated in a fleshed out world and story, which makes it a more interesting ship than ships which are just "this boy and this boy are cute". It's also closer to canon than most m/m ships ever get to be (outside of straight-up BL/fujo series) which gives it a lot of appeal.
Also, it's probably the best shota ship.