Because they are now potential opponents for people in the ring. It's called selling the concept of the draft.
I can see it for stuff like Kane/Big Show and Melina/Smackdown Divas, and even w/ Rey and MVP. But I don't think we're going to get a program between the two pairs I mentioned at any time, not only in the forseeable future, but ever.
You don't, but I'm sure there are marks out there that do... and remember, they are and always will be the target audience.