Series games correlation

I've been playing a lot of ranked lately and I've noticed something, my team mates and enemies are generally of the same skill level until I reach my series. Then 9 times out of 10 I have someone who is excessively toxic/uncooperative/un-knowledgeable or the game is an absolute stomp in my team's favor. Does Riot purposely put worse people in series games or is this just a very unfortunate coincidence? After completing my placement games, the only games I've lost in ranked, except for either 2 or 3 due to connection or being beaten by the other team because they were better, were series games. Has anyone else experienced this?