User blog comment:Jkl9817/Yet another serious blog/@comment-995188-20120427233958/@comment-1874924-20120428001732

The reasoning behind leaving the Collaborations category off the new library template is that the front page's target audience is mainly people who are new to the wiki, and those people probably won't care whether a given story has a single author or multiple authors. Furthermore, Collaborations and One-shots are currently the only front-page categories that are defined by a story's structure, rather than its content. (Indeed, I also suggested dropping the One-shots category for precisely that reason.)

While it's true that the Crossovers category doesn't currently have many entries, I think this wiki has a lot of crossover stories that haven't been properly categorized. After all, any competition story that draws its characters from other franchises is a crossover. And while there may be very few finished crossovers (indeed, TDI-G&S may be the only one), the Collaborations category has the same problem.