Minimum Ranking

Unsure if there is a reason why the current Ranking system is the way it is but here would be my question. Why is there no minimum to bronze Ranking? Why not have the bottom 10% or so of ranked players just be unranked and do a similar form as masters does where the top so many get promoted to b5 every day? Just seems odd to me that you are garenteed bronze at minimum and I have to imagine that makes bronze more toxic just due to that fact that you have nothing to lose. You can troll in bronze 5 and still ruin games for people who actually try in b3 or so. So for example. Current b4 and lower becomes unranked Current b3 to s5 becomes bronze And so on