Why are loss streaks so heavy

I used to go on pretty good win streaks with good teams and was able to get to gold 1 20 lp but i went on a loss streak and in two days i got demoted to gold 3 after 1 loss at 0 lp. Why do loss streaks happen for the mostpart i do pretty good but we still lose it just seems like when you start losing you get shittier teammates than the enemy who are more likely to throw.