Sure a lot of fanfic writers are squealing 14-year-olds who want attention (this is also true of people who decide to ditch a well-liked character for no other reason but to show how different they are, just to get that extra attention), but I think most of what drives people to write about those pairings is what you also refer: pairing up their favourite characters.

I for one, only read the occasional fanfic, some with canon pairings, some with those odd-pairings. Some of the odd pairings simply don’t compute, but to each his/her own.

Raquel;
I have seen a lot of drama come up from the Harry Potter fandom and while it’s not a video game based one, I did notice a lot of pairings in it were intentionally supported for drama. I’ve yet to find a good example for a video game character pairing that was intentionally done like this. There are a fair number of good fictional works online about oddball pairings and I’ve read them, seeing some plausibility to the relationship’s existence. They are a rare gem amongst the rubble of the Internet, though.

Klear;
I agree and I disagree with this comment. Pairing is a common concept in every fandom and it’s true, they corrupt a lot of things. It’s always painful to search for a favorite character’s image and see all the artwork of them with people they’d never love. However, like I mentioned to Raquel there are always a beautiful fictional work that works well. Some games though do not need pairings… yet, people manage to come up with them. Have you seen all the Red vs Blue pairing ideas floating around there? Yes, there’s a fandom for a Halo parody. It’s crazy.