There is also more to it, people are quick to blame support, be a tank or a healer, if anything goes wrong, it doesn't matter that the DPS ran in too far ahead, doesn't matter that they were ignoring battle mechanics, that they couldn't keep it together for 5 minutes, something goes wrong? it is the support's fault.
Now, there is more to it, and a good group in any game will be able to identify when it's not the support's fault, but even in GW2 in pubs, I had a situation in KO where a person glitched out during the transitions and wasn't launched right, and landed full dead, in a run where people were ignoring a good chunk of mechanics and making it a lot harder for me, the first thing someone did was to say that the healer, in that case me, was a kitten player.
And trust me, nobody likes to be on the receiving end of that chunk of vitriol, and this is coming from someone who likes playign Support normally, when things go well enough.