I'm willing to bet you've heard more than one band and thought, "that guy can't sing." Maybe you even liked the music, but the singer was just so awful it ruined it for you. It's not simply the domain of local bands who couldn't find a decent singer off Craigslist either. Some popular bands have singers so bad they can ruin the whole band, though more often than not it can thankfully be overlooked.
It's hard to understand how it happens. Maybe they just really like the person, or maybe they just really couldn't find anyone else and got stuck. No matter how though, it's a recurring issue, and these are just a handful of the bad singers you find fronting great bands.