Are there not enough supports?

Most of the time I get matched up with high gold - low plat since I'm a plat 5 support main. But sometimes I get matched up in or against a total silver - low gold game is this normal or are there just not enough supports in the Q sometimes so they take one from a devision higher?

I have a positive win/lose ratio (~55%) and my mmr is about right for my devision so I don't know why this happens. I don't really like playing with silvers, not that they are all bad it's just that the games drag on and on and on because they don't know how to finish through objectives only through kills.

The only time I find this really annoying is when it happens in my promo's, they exist to prove you have become a better player in League and should match you up against higher tiers or the same as yourself but that doesn't happen and I don't really learn anything out of playing with silvers well maybe some new ways to verbally abuse my teammates or enemies.

I think it's also pretty unfair to the enemy team because most of the time I just 1v2 the enemy botlane as Braum and get flamed by the enemy team as a result because I'm "tryharding".

tldr: Not enough supports? Matched against or with silvers, hate my life.