AJ Lee was in an Official Couple or had Ship Tease with a grand total of six guys... one year. This was bound to happen eventually. Of those six guys (Daniel Bryan, CM Punk, Kane, John Cena, Dolph Ziggler, and Big E. Langston), her most popular pairing is with Punk. In fact, it's the most popular ship that isn't with Original Characters or slash in the last few years. It's strange, because Punk and AJ's storyline ended over a year ago, they are currently on "opposite" sides (Punk had turned Face after his 2013 return), and AJ was in a happy relationship with Ziggler for the better part of 2013. They haven't interacted at all since late 2012.
Slash itself is wildly more popular heterosexual pairings, because the majority of heterosexual pairings in the fandom are not with the Divas, but rather with Original Characters. As one can tell, many of these stories are... lacking in quality (mainly because many of them are poorly disguised Mary SueSelf-Insert Fics), and slash stories are widely perceived as a whole as better when it comes to quality. The fact that wrestling boils down to good-looking, half-naked men rolling around while often times covered in sweat does not help, with all the Ho Yay and Foe Yay abound outside of the actual matches.