A lot of "trash" music sells. Chance isn't selling because he was always FORCED. He had the Grammy committee changing the rules and categories. Not necessarily him per se, but rules were changed because of him. He was in commercials. The impression that he was some superstar was pushed and still had people saying "who is this and why should we care".
I don't think it had anything to do with the DNC. Dude was pushed because music these days is slack on stars and they saw this "wholesome", Gospel schtick and saw potential. Didn't hurt that his family was cool wit the Obama's and Kanye was featuring him.