Players are making the game more snowbally than it actually is....
Ever hear the old saying, "Argue for your limitations, and they will be yours." This basically means that if you have a bad attitude which causes you to set your goals low, well sure enough, you will meet those low goals and nothing more.
The reason LoL seems more snowbally that it really is is because everyone believes in the "Snowball Meta", so as soon as someone dies, the "losing" team suddenly wants to throw in the towel. I know this is true, because I have seen A LOT more early "gg" and "ff15" in the last couple months than prior to that. People are going into games expecting to win or lose on the first death, and their mentality instantly goes in the drain if they are on the death side. So with people ready to lose right away, they play more poorly, and sure enough they lose...because of attitude, not because Trist or Lulu is OOP atm.