Support isn't hard to play but it's hard to be a good support
You see, even plat+ players mistake the role as just "walking around" sometimes and end up having horrible builds, I know when Tobias Fate was trying support he built Ancient Coin over a Relic Sheild on a tank and the whole chat screamed at his idiocy (he admitted he was trying to find a new role+champ to try and have fun with climbing again)
It takes a good support to be able to harass, protect their adc, be WILLING to protect their adc, know when their adc is fine so they can roam/ward, and know when their adc is useless so they can just roam and try and get other lanes ahead, even building the correct items takes a good amount of expereince.
It's also an underplayed role because 'I need damagus to carry my team WaAAAH' when on Sion supp I usually end up dealing more damage than my "carries" with nothing but an IBG and some tank items.
As the previous person said, it makes sense for any role, though that probably means those people who can't play a role at a borderline level need to practice them a little.