they simply shouldn't exist in the first place.
they're just trying to coddle you by making it more difficult/rigid for players to keep what rank they've earned so its an "accomplishment" - (just google video game psychology, going up 1 division creates a huge lasting reward for your brain)
because watching a number between 1-3000 go up or down after every match is boring.
they prevent "feels bad man" experiences when you go from silver 4 down to bronze 3 too quickly. it makes you feel like trash.... even if its justified through your play.
its ok to climb up or fall down 3 divisions overnight. without having to play 100 games to do it.