Whats wrong with the matchmaking system?

As a returning player i feel like something has happend to the mm system. At first all seemed normal but after I've climbed and won most of my games i started to lose some and i thought "thats just unfortunate to get placed in the same team with bad players". But after those games I just started to lose even more and yeah a couple of those games I didnt do very well either, but for the rest of them it has been mainly because of my teammates with way lower skill level then the enemy team. And that got me thinking if riots mm intentionaly puts you with worse teammates if you've had a great climb. I started in silver 3, got to silver 1 with 72lp, and now im back in silver 3 mainly due to increadebly bad teammates. In 20 games I would asume that I win maybe 3 or 4, and thats when I get decent teammates and im able to kinda carry.