My problem with autofill

Ok so i wanna talk about autofill. If i am in lobby then in the bottom of the lobby it says "Autofill protected" then when i come to champ select i am autofilled to support again. Why? And cant autofill just be deleted from lower ranks because waiting 2 min isn't that big of a problem. And then when i come in game i suck and feed and then get blamed because of autofill and i lose my ranked games and i end in bronze at some point