Why are promos still a thing?

Lets say you only get 8 lp for a win -because you're MMR is so low- and lose around 15. You are at 0 lp. You win 13 games in a row, YAY YOU. You then lose two. Not only are you not advancing in ranks with a 87% winrate, but you are punished even further by losing 4 win's worth of lp. Of course, you have to have lost a lot of those matches to get to such an extreme ratio like that, but even still for the people gaining 18 lp and losing 22, its just a big slap in the face to win so many in a row only to be back where you started for losing just two.

Furthermore, why do promos intentionally set you up with worse players to complete your promos with? To my knowledge, promos ignore mmr. Sure my team is all gold3/4, but their mmr can be straight ass in promos. The "feeling of accomplishment" when you are victorious is the reason the promos were put into the game for (riot's go to answer), but its more like "the feeling of luck that not each of my teams had too many ragers/afks/bads."

Seriously, wtf is up with these and why are they still in the game after over a year of people complaining?

Guess which game on my match history is a promo game.