I know that this is so 2013, but what is wrong with promo games ?

I really want to know, i didnt lose a single match until promos, and in my GOLD 2 promos i get a Silver player that decides to int out of nowhere, taking jax with ghost + swifties and in the next game 3/10 Warwick who also just decided to show up and give enemies free kills ? Games SHOULD be 50/50 win chance (although it's not like that, one team has alot bigger chance to win), but what's up with promo games ? Is it 40/60 or something like that ?