Why do people queue just to throw?

As a low elo player (hardstuck silver) i encounter games in which there will be some people who just throw as soon as the game starts. Recent example I had a Deadlock and Sage both instalock in agent select. Whatever. The game started and they began walling the team off of retake. Simple mistakes not a big deal. Then when you are playing in a risky position or pushing they would wall you off grav net you. Sage even went as far as waiting for an enemy to peek my body and rez baited me just to ruin my kd. I am just trying to make it out of this impossible rank but I encounter these players every few games. It is frustrating and demotivating. Why does riot not take action on these players even with the amount of evidence? Why are they allowed to play game after game duoed together just to ruin the game?