I can't imagine how Scott deals with all the negative publicity. Can you imagine knowing there are articles bad mouthing you, websites voting for you because they think you are the worst even if during some weeks you aren't, talk shows bad mouthing you because they liked greaseball better? Judges showing favoritism. It would be pretty hard to be all smiles while knowing all the above. It might even make one a bit sullen, quiet and maybe even a bit defiant.
That could apply to all of the performers, not just Slingblade. The difference is the others (with the notable exception of Mikalah) seem to have a basic grasp of good manners.