What is a premade ? some players with a vocal maybe playing the pvp how it should be played.
They win because players aren't waiting a regroup, don't cooperate and feed endlessy not waiting to be enough to fight them in most case.
If a premade is too good and attack your base, you can even just run and take the base of the enemy, it will make this premade retreat because if there nobody to fight, there no reason to stand in the enemy base.