Why does Riot match you with losing teammates in your promos?

Can't we have a ranked system that, you know, just puts you against regular players with regular streaks and just let the promos serve as just a 2/3 barrier rather than a "carry this 1v9 2/3 times and then you can rank up" style matchmaking?

I understand that Riot likes to pressure people who are climbing into doing better, but if you can carry 2/3 games where your entire team is sandbagging because they're on their 4th or 5th loss in a row, then you're probably 4-5 divisions lower than where you need to be, honestly.