They were down until Cena chased and Cena/Ace was shitting on his reign, Mania time when he and Jericho were reduced to third fiddle as they got beat horribly by the streak and Cena/Rock in terms of viewership, got dwarfed by Brock's two return feuds, Kane's return outdrew him and I could go on. The fact is he's been carried draw wise in comparing to other guys. It's a risk with ryback, but really it is an unknown they may have to gamble on.
They have went with every combo Punk could possibly be as the guy: clean drug free guy, crazy guy that snapped on Jeff, cult leader, nexus leader, rebel bad ass who is outspoken, good face who works for respect and plays the victim after being disparaged and having his skeletons brought out by Jericho, and now crazy ass crybaby ala Austin 01 with Heyman in place of Vince.
They know what Punks ceiling is, and they also know 3 hours or 2 hours that he isn't the major gainer of the show, he may be bigger than the others, but it ain't like being the 2 that Dave, Edge, Taker, HHH, and the like can pull off so they resort to bringing guys back or the part timers and Cena sparking the show all year and drawing for him, main eventing over the champ because he is not a tier A guy himself.
Ryback with his momentum could be the surprise they need to find stable balancing of the scales so there is two number 2s as opposed to a number 1 in Cena, a gap, Punk, and a gap to the other full timers