Why did riot make the game team based?

I don't understand why this game was changed to where if you were good, you could climb on your own and not worry about your team. Now it is more or less based around being lucky in getting good teammates rather than your skill level. I understand if you're good at the game you can be a team player, but it gets to a point where that is almost impossible for you to do because it depends on those four other players in the game.