Here is why nobody wants to play supports:

1. Significantly fewer options when behind. When bot lane starts to become a lost cause or my adc starts putting blame on me, I like to roam at this point since there's little I can do to help him. This, of course, will get much rage and ire from the team, even though Top or Mid can and should roam if they fall behind.
2. Significantly smaller "acceptable" champion list. There are maybe a dozen champions you can pick for the role without getting flamed, and then automatically blamed for everything that goes wrong. Top and Mid have a huge array of champions to pick from, between mages, to assassins, to tanks, to adcs, and so forth. Picking anything other than the established meta gets you in trouble. I am a LeBlanc onetrick, and almost every time I pick her in support, I carry from bot lane. But that doesn't stop the team from flaming me the entire time, or getting automatically blamed if we lose, even if all other lanes feed. But hell, if I want to go Top LB, or even ADC mid LB, no one even bats an eye.
3. Very strict playstyle. There is only one acceptable way to play support, even though they are meant to provide help to the entire team, rather than just the ADC. You are given much less flexibility than any other role in how you do your job.

These are just a few of why I hate playing support, so maybe Riot can understand why its such an underplayed role.