User blog comment:ObiWanCokeNosey/Someone want to explain something to me?/@comment-26018514-20150422165122/@comment-24891101-20150422173036

More or less this. Narrative viability uber alles (this does not mean it's a healthy ship, merely interesting and canonically supported).

I would add if the relationship makes sense given the archetypes, which have some degree of predictive power.

Homosexual relationships have a higher energy barrier to overcome, and are therefore much less common. This means that there must be some form of circumstantial evidence that the characters are of the appropriate sexuality, since the null is heterosexual. The other reason is backlash against the overrepresentation of such relationships with no rhyme or reason in fanworks in general.