Because for unknown reason, players are allowed to first time the brand spanking ass new champions into ranked, solo losing the game on his own because he goes 1/10 and doesn't offer anything for the team what-so-ever because he's busy learning what his abilities do.
I seriously do not understand the thought process behind this, but literally everyone on our team was upset with him because he obviously didn't take the game seriously. If he did, he would've picked something that he knew how to play, but he didn't. His match history is filled with Karthus, Katarina and Yasuo, but then decides to first time Sylas and fuck over everyone on his team.
To be completely frank with you, this shit causes a toxic environment. You should NOT be able to play a new champion into ranked until they're been out for at least 2 weeks, period. This exact same thing happened to me 4 games ago, my teammate locked in Sylas, went 3/11 and we lost the game.
Trying new things is for normals, not ranked. Have some courtesy for your teammates.