I have a theory about this. There are a lot of people that come into QaF with it as their first fandom, but there are also a lot of people who come into it already having been in fandom, and already having been a slasher.
Slashers are attracted to it, because OMG slash is canon! But they're so used to searching for subtext (and you have to admit there is a lot of UST between Brian and Mikey) that even though there's a canon pairing, the subtext calls out to them, and they end up shipping Michael/Brain.