I was playing a blind pick game the other day. In champ select most of us called our roles as usual, but there were 2 guys who were slow to respond. The only roles left were ADC and support. One guy who was already locked in said: "so, which one of you is the slave.....errr, I mean support?" It was obviously meant as a joke, but remembering it in the context of this thread makes me realize his statement wasn't far from the truth.
This is how the majority of the playerbase thinks of supports: they are slaves to the rest of the team. They exist only to serve the team's vision needs and provide occasional cc and peel. Their lives are worth less than every other member of the team, and they are punching bags for the ADC during lane phase. With this kind of mentality among players, it's no wonder that no one wants support. Who would want to subject themselves to that?
Obviously none of it is true; supports are the hidden carries, allowing the playmakers to make the plays and putting the rest of the team on their shoulders. But no one except support mains see that; everyone only cares about their flashy plays and their "mechanics" and getting all the glory for themselves.
You want to know why the support role is in such dire straights? We, the players, made it that way with our ignorance and selfishness. As long as supports continue to have this negative stigma attached to them, the role will continue to suffer. What needs to change is our concept of what the support does for the team.
Supports aren't just slaves (though they are certainly treated that way, especially in solo queue). Until people are willing to accept that fact, nothing will ever change.