Because people LCS Zombies can't think for themselves, hence Zombie. They don't want to find a champion whose character and playstyle they like, they just copy whatever a streamer deems as "Broken" or "Freelo".
These Zombies often have the marker of their favorite team/streamer in their username (Example: TSM Fatbaby420) and spew out copied catch-phrases such as "Rekt", "The damages!", "The Jukes!" (While playing LB, btw), or "Madlife hooks!". Completely unable to use their own vocabulary for taunting the enemy.
Newsflash, you're going to play a hell of a lot better and enjoy yourself a lot more if you choose to play and learn a champion you actually want to, rather than copying someone else just because they had a good game as X or Y champion.
I look at these streamers and LCS hype and I ask myself. Why? Why should I care? Why would I copy someone else when I can make a name for myself?
Be original, don't be an LCS Zombie. Nobody likes LCS Zombies. Except other LCS Zombies.
/end rant