There are actually support only players, filling mid as secondary, and getting mid quite often. We all know mid is one of the most popular roles, and that support is extremely unpopular. If that's the case, then how come these guys are getting mid?
Yes, shit happens, but when this kind of shit happens, then you can tell something's strange with the matchmaking systems.
At first I mained support because no one takes it... someone has to do the job. Then I found it fun because you're not really playing League of Legends, but a slightly different game where you it is mostly tactic, and hoping that your teammates do something... very little mechanical skill involved. Perfect for people who has garbage mechanics and excellent tactical skill (trust me I should belong in bronze and should never have any badges... but huzzah for supporting and how I can get it so easily). Heck, because of how much tactics you actually need, most people who are not Leona/Thresh/Blitz and is supporting loses my games, and I don't want to see any of that.
I have no problem with not being able to deal damage and not taking kills. I have no problem with getting less exp and gold than everyone else (I mean no shit, they don't farm). Heck, I have no problem being the "ward bitch" because people usually don't know how to utilize those properly and effectively anyways, even though I don't like the Sightstone nerfs. Supporting is mostly playing around your enemies and making sure they have the worst experience possible by not doing damage; that shit's already fun. Even better when you're playing that's perceived as "weak" then kicking their asses in the end anyways. You literally get rewarded for how well you pull off your tactics, not mechanics, which is something I really loved about maining (Lulu) support.
Shitty teammates that don't even know what on earth is a Lulu support, so therefore not knowing how shit works? Oh well, I see that shit everyday, move on. Shitty teammates that have no clue on how to avoid Blitz grabs or something? Pfah, I got plenty of other allies to babysit; it's not the end of the world! Lost lane, or game? Fuck that, I can't win every game, just try to do better next time. All that doesn't make me hate supporting; it is still loads of fun.
But hey, that's just me; that's just my definition of fun. It's definitely different from the majority of players.
Or just take a look at MMO's; people playing "support-y" classes are uncommon, though heavily needed. At least 3/4 of the playerbase in MMOs play some kind of DPS classes (including me), because killing and beating up shit is fun. However, as support, you don't get to kill shit. You don't get much spotlight. You can't even handle on your own! It is no surprise that the support role, in general, is unpopular.
Unless they get to deal tons of damage (Annie/Brand/Vel'Koz), get lots of glory and be able to look flashy (Thresh/Leona/Blitz), or even create an extra source of gold/exp on the map (which is not really possible), the role in general would be unpopular. "Do less damage than your teammates, function even with reduced gold/exp, rely on lots of teamwork (due to less damage) instead of just individual skill, and just save your (probably stupid) teammates" is already unappealing enough for a lot of people.
2 cents for ya, also explaining why people just don't play that role anymore. Unless this game gets some kind of overhaul, support will remain unpopular.