What's wrong with Matchmaking?

So I'm on a winning streak. Doing pretty well for myself. Fighting people around the same skill level and coming out on top. Now i'm legitimately fighting with terrible teammates, in uncarryable games. It's legit impossible.

I got an S this match.

https://i.gyazo.com/295372df263e33e860a16e3a1657af59.png

I beat Riven without dying to her once. Only death was at the end when our team surrendered.

What am I supposed to do? Why even create these pairs? This matchup was so dumb.