Platinum Level Toxicity and Trolling

Last game I played, I encountered a very immature Wukong on my team.

After playing a spectacular team-fight without any losses, we proceeded to push down the bot tower, and I, Yasuo, went mid lane to take mid towers.

There were two enemies bot lane, of which Wukong wished to engage on, but I was not there. I defied his "authority" (that he thought he had over our entire team) to get a mid tower.

After this, Wukong proceeded to essentially remark, "yasuo doesn't group to teamfight gg" and disconnects from the game.

He couldn't handle someone not listening to him. Why is this possible? How do players like this reach Platinum without being banned?

The game totally destroyed my morale. We would have won if he hadn't disconnected.

Thoughts? Am I just unlucky, or is Platinum just a trolly tier, full of hormone-enraged children?