Because you want to see Voyager's Chakotay get his hands on the Sentinel's Blair's butt?

Well, the people who only read slash only for the sex will be thrilled. Of course, those who also read every story posted to alt.sex.gay.moderated are not what I'd call a really discriminating audience.

On the other hand, maybe you have an idea that Blair, after being sucked through a time warp or something else cheesy, finds himself on Voyager and meets Chakotay?

Maybe you wonder whether or not the presence of a gifted and trained Guide might activate latent Sentinel abilities in the Voyager's First Officer? (I hope no one wrote this - I've tried hard to avoid using examples from Real Stories....) You wonder how Blair would react to having a new Sentinel and one so different from Jim? How does the Voyager crew react to having the Guide on board, and to the changes in Chakotay?

That's an Xover worth writing. And worth reading. Because you're doing what fanfic is best at - you're exploring the interaction between characters based upon their personal situations. You take Blair's personality, who he is and plop him down on Voyager.

Of course, if they have hot sex, too, then everyone will be happy, right?

The key is to decide WHY you want these two characters together. If it's just because you think they both have hot bodies and want to picture them in your head getting it on...well, that's okay. But bringing personalities and issues from each of the character's "universes" into the mix will produce a much superior story.)