Because Smackdown is the better show and that would completely fuck Smackdown over. Smackdown is already stuck with trash like Ambrose, Dolph & Bray in the upper midcard, don't need to take AJ away and replace him with even more trash.
This basically.
During a Draft I am thinking only of the good of Smackdown.
Also in turn, AJ deserves to be on a good show and not a shit show like Raw.
Strong odds are that a show prominently featuring AJ is going to be strong. He's not quite incredible enough to turn 3+ hours into 2, but there are so many new matches to look forward to if he is indeed moved. Much as Reigns makes sense, it does seem unlikely after the Taker win and how he was presented Monday, but that would really leave Smackdown with a hole on top as it'd be losing the babyface and heel that have carried the show since the split. Perhaps Nakamura is given a chance to fill the 1b babyface role, but depth looks to be an issue.