Why will they let Cena beat The Rock?

Cena should never beat The Rock. The Rock has always been a legend and always will be. And since Cena lost last year, you know he'll win the match this year. Why can't they just make Cena turn heel at wrestlemania. If that happened I wouldn't be upset about The Rock loosing, because atleast us fans got a shock out of it. Why do they have to make Cena look like a legend when he doesn't even deserve it?