So much of our real-world sexual behavior presupposes the fact that one's physical form is difficult or impossible to change that it's easy to forget that in a fantasy setting with transformation (or even just illusion) magic only personality would matter. Everything else can be fixed by Alter Self.

(I expect that if wizards are fantasy nerds, they don't have the same problem of an unbalanced male:female ratio that real-world nerds do. Or maybe they would have the ratio just as unbalanced but in the other direction, with almost everyone being a Drow femme fatale.)