So why is my MMR affected by the teammates I get and not my performance?

So lets say I get like 15 kills a game and die very few times. However, I get some kids on my team who wear helmets and drool on themselves while playing League. Therefore when they refuse to listen to pings and die costing us Baron and game, my MMR drops. Why is this the way MMR works? Maybe this is something you should look at when working on the "problem" that you claim to understand about higher skill players not being able to carry helmet wearers.

P.S. I love how Riot claims to understand the frustration of carries being unable to carry, but the only suggestion that buffoon came up with in the video was "to increase shutdown gold." Like... WHAT???? What does this have to do with being ahead and carrying your team LMFAO, if anything this makes it harder to carry when the enemy team 1v5's you since you are the only useful person on team. How did these guys even get their degree?