The Rock’s WWE Championship match was announced over six months ago, at Raw 1,000. It would be crazy to change it now, right? Crazy enough to cause controversy!
From the perspective of a booker, having Rock penciled in for a WWE Championship match at the Rumble would be a massive headache.
Having him lose at the Rumble is extremely tricky. Trying to think of a way for him to lose (or simply not win) without looking weak or diminish his momentum? Screw that noise.
Many have assumed, with some justification, The Rock winning at the Royal Rumble is a foregone conclusion. If he does win, finding ways to have him be a part of the show on TV and house-shows where he can’t make it would be a booker's nightmare.
Plus, if/when he beats Punk, where does he go from there? To John Cena, that's where.
No matter how big their respective star powers, surely even Vince would have a few reservations about having Rock and Cena main event two back-to-back WrestleManias, and that’s really the only way they can go if Rocky beats Punk.
Backtracking on Rock having a WWE championship match at the Rumble would be a risky move given it was announced so long ago. However, there are plenty of ways to get similar value out of The Rock at the Rumble.
Rock vs. Cena II at the Rumble, anyone?