Why series forgiveness is so good.

I don't know if i'm the only one, I'm probably not but either way, whenever I play ranked it goes fine. I usually duo or trio queue with friends we play and win, occasionally lose, but mostly win. Then I get into my promotional games, and holy hell... It's like all of the people who play ranked are like "ok, time to let my friend or 5 year old cousin play". I go on 5 or 10 game wins until I get to series then I lose. Then I win and get to series, then I lose. This usually repeats itself until I either lose and go to 0 lp or get demoted. I went from Silver 1, to Silver 5, back to Silver 1, to Silver 3 and now am perpetually stuck in Silver 2 hovering around my series. It's not like I play any differently, consistently it's the random people in my games that just go full blown feed lord i'm so glad we have the series forgiveness to get that free win when we get back into series, or else I probably would have tilted my way to Bronze 5... I don't understand it.