Sandow yes, got over as a comedic figure, but once over zero was done with him or even attempted to be done with him. A trend that is not limited to Sandow.
In that instance, fans like to cite the failed cash-in as the moment that ruined his career. In truth, he wasn't good enough to carry that role, largely because he worked a softer style, when main eventers need to raise it up a notch. While he did well with the Mizdow gimmick, it left him in an awkward spot. He wasn't a natural babyface, 10 years of working as a heel put him behind a lot of other wrestlers and the character needed a change.
How over was Riley really? He had cool theme music, fans were into the Miz turn initially...but the guy was just another Virgil. There was nothing compelling outside of being Miz's best friend. Sometimes if you're a good worker, it can make up for the lack of personality. In Riley's case he was untrustworthy, blowing spots all over the place, in particular in the 2011 Royal Rumble. The WWE seemed keen to forgive and forget, having him feud with Dolph over the US Championship, until he had this god-awful match with Swagger. Riley managed to botch the gut-wrench not once but twice in the single night.
