Why does the ranked matchmaking system try to push me into defeat games? making my MMR take tanking?
So I've been playing only OTP
in ranked and started adopting to learn more about the macroplay in my games. Although I'm still not exactly good with it still. I understand all of kha's mechanics and I can carry quite well when fed as kha'zix or when I snowball lanes especially when I've camped them alot in early game; however I've started to notice even if I camp lanes e.g. top or mid either the bot lane or 1 of my camped lanes suddenly ends up int feeding or making simple mistakes over and over resulting into a loss game.
As a result I went from S3 50lp to demoted S4 32lp and apparently now have an MMR of bronze 1 when only 2-3 days ago I was S3 MMR.
Take for example my most recent game my team comp was:

VS

I was carrying with 13/3/0 and we were trading pretty well, I had shut down mid and gank top however lux would get fed up if ahri would stick around and get greedy on cs at low health so that's typical and our poppy would often try and push on her own and lead to be inting enemy team due to no vision.
However by mid game we had not taken any turrets and the enemy team had taken 4 plus the 2 drakes. What ended up happening was the enemy lux would carry their team through misplays on my team but I just don't understand even though I shut down 1 almost two lanes that suddenly a couple of deaths from 2 champs can lead to a reversal of the game situation.
I notice this alot in many of my games now. We do well in teamfights but then the team doesn't get any turrets resulting in us being pushed back whilst enemy takes more objectives.
I know the matchmaking system is meant to work against you to lower your WR to under 50% but I have to ask why does it then decide to push it further to force me into even lower divisions and matches myself with teams that even if I do carry the game still ends up in a throw?