Why do I get so many toxic teammates?

Trying to rank up but most of all, trying to get a fun and challenging experience. I always seem to have people that, either go afk, go feeder, and all around is toxic.

I like to play LoL for the competitive scene, not the nerds pros level, but at least matches that require teamwork and communication, tactics and strategy. But every time is always my team who is toxic.

How do I prevent it, duo just makes the game from 1v9 to 2v8, but we still get 3 toxic teammates, any ideas? Trying to not leave LoL since it's better than dota, and hon is dead, but the toxic players I always get, makes it boring.