Whats the point in locking a large amount of the champ pool in urf...

IF YOU HAVE TO OWN THE CHAMP TO PLAY THEM IN URF a few are free right now like but why lock away like 40% or so of the champs and only allow the ones with Christmas skins,which if you own a champion that does not have one,that is one less champion in your urf roster and then you only have like 15 champions to roll from