What is the point of winning an arbitrary amount of games (promos)?

We usually only need a 55% win rate to climb so why in promos does that number automatically jump to 75%? I say 75% because you need to win the game to get you to promos and then the 2/3 to actually make it to the next division. It makes no sense to me. My suggestion would be to just remove promos altogether and as long as you have a 55% win rate you will continue to climb. You shouldn't just get shut down because you can't win a certain amount of games at a certain time.