Main supports getting burned
I'll state the obvious: The goal of league is to be able to carry your team.
That said, few want to play support when it is hard to focus on support and trust that the rest of your team will carry.
Riot has gone the extra mile to provide reserved position slots: If a player chooses support for a match, the next match will give that player preference for the position desired. However, that's exactly where it stops.
If a player prefers to play support for the shorter downtime and maybe just prefers to support, Riot still penalizes that player by forcing them to carry bad players. This quickly drops the player into elo hell.
Rant ends.
[zombie-nunu-bummed]