Because of the way that Cena bumped and sold Ziggler's offense. He made it look believable, and like his offense was a real threat to defeat a 9 time champion. Cena could have steamrolled through Ziggler like he has bigger stars in the past but the match was competitive and back and forth. HE even hit one of his signature moves in the fameasser on Cena, and Cena sold that he was going to lose the match until the last second when he rolled the shoulder up. He also locked the sleeper in on Cena, and slipped out of the FU, which many opponents have never done.
A match can be booked evenly between two people, and the execution be bad, and its a poor match, regardless of how its booked. Its the two wrestlers in the ring that make the match what it is, not vice versa. Cena as the better and more credible wrestler, made Dolph look like gold because he made it seem like Dolph had a chance to beat him in the match. Cena's aggressive, but he allowed himself to succumb at times to Dolph's aggressiveness as well. He chain and mat wrestled with Ziggler as well, which is one of Ziggler's strengths. So when you play to your lesser opponents strengths, you make them look good.
As for the heat that was generated, you can attribute much of that to Vickie, but the level at which the heat was received was beyond anything ever drawn for either Dolph or VIckie. Why? Because it was during a John Cena promo, the top babyface in the company. When you look to draw heat for someone, an easy way to do it is against a hot crowd who adores said babyface. The crowd was extremely pro-Cena last night, so much of the heat, whether started by Vickie or not, transferred to Ziggler. Its really that simple.
As for Ziggler, he's had a phenomenal year. He took the IC title off of Kofi Kingston and had a fantastic set of matches with Kofi on Smackdown leading up to and on the Hell In A cell PPV. He followed that up with a great series of matches with Daniel Bryan as well. Even before he had won the IC Title, he was involved in a mini-feud weith Christian, in which he even defeated Christian once. Before that, he had a series of good matches with Rey Mysterio, and also with John Morrison. Dolph's been a great champion with an IC Title reign thats lasted almost 5 months. He's turned back Kofi, Kaval, and Swagger amongst others as contenders for the title. He's developed into a talented performer whose work in both tag and singles matches have often been the Match Of The Night on Smackdown consistently. It shows the faith they have in him that he hung for Cena for 13 minutes and pushed him to the limit. Even in a loss, Ziggler came out looking better for it.