It's really the volume and impression.
There's so many canon pairings of other main characters, that Shiroe himself's situation is less focused and trivial.
Pretty much every other prominent guys and gals gets a mate.
It also helps that while Shiroe is the protagonist, Log Horizon leans towards the nature of
Ensemble casting with less focus on the protagonist.
Well, ignoring Sojirou who needs to explode and die.
