Why does ranked use the system it does?

I recently got to silver with an 80% win rate. The next day I had 25 LP silver V and the next 3 games all the lanes ran it down while I was adc. I did fine compared to my team but as an adc I cant carry when the kled is 7/1 and no one is capable of peeling or protecting me.

So why does riot make it harder for good players to win games by placeing them with horrible players? If anyone has a good reason please tell me.