As you get closer to your highest SR, it places you in more difficult match ups. There was a huge write-up on the inner mechanisms of comp on the competitive overwatch subreddit a while back. I'll try to find it.
I would love to read this because its not like competition gets better, I more than hold my own it just seems like my team is really really bad every time. Anytime Im close to breaking my SR season high, I am always on the team that gets completely steam rolled. I wouldnt care if they were close games, but theyre not and thats whats most frustrating. Its like hey you won a bunch of games so were going to stick you on a team with really bad players.