Why do we still have promotional series?

I feel like if you have a positive win rate you should be able to climb elo. With promotional series you have to have a 75% win rate to climb. You have to win the game to put you into the promos, then you have to win the next 2 out of 3 games, which means you have to win 3 out of 4 games or 75% win rate. This means that for some people who lose every promos it could actually mean that they cannot climb with a positive win rate. Which is a dumb concept all together. If you win more than you lose you should rank up instead of getting stuck. I think promos should be removed or changed a little bit. I have no idea how they have lasted this long.