The ratings didn't sag. Bryan's segments were pretty much always the highest-rated for the months that Cena was gone, and ratings were high at the start of the whole Corporation thing. Summerslam's buyrate was disappointing, but it was Bryan's coming out, not his apotheosis, and it was close to SS 2011, which was headlined by CM Punk, who's now their #2 guy after successfully being pushed with the title for a year. If they actually blame Bryan for Night of Champions/Battleground/HIAC, and not their shit booking of those events, I'd be surprised, as they very manifestly didn't consider those to be anything more than high-budget house shows to tide them over until Survivor Series.
I think they just saw post-SS as a poor time to try and push a new star, given the lull period (in terms of ratings/business/general giving a shit) that follows it, so they had him beat a Cena who had to leave anyway, given his injury, gave him a main event storyline while trying not to overexpose him, and shifted the big push to a company loyalist likely near the end of his run who had the acting chops to get over, the name recognition to get the fans behind him in a short period of time, yet could go away when they needed him to. I have to think they did eventually intend to push Bryan, given his beating Cena, three months of main events, and then being folded into the protective Punkverse, but whether they actually get back to pushing him is another matter entirely. He's still VERY over with the crowd, as tonight showed, and could easily be credible, say, winning the Rumble, and you could easily get Cena in there and make a triple threat if you're truly worried about star power, but perhaps the SS buyrate scared them off of the idea of making him the #2 babyface.
Who knows? I guess I'll just try enjoy this Big Show thing, enjoy the fun of Bryan and Punk teaming together, and hope for some more watchable matches like we got tonight.