Ranked tier placement?

I started in Season 3 and was placed in Bronze 4. I never played ranked, I only played my placements. In S4 I got places in bronze 2 and only played my placements. This season I just finished my placements 9 wins 1 loss and was placed in Silver 5 can someone explain the reset to me? Why does my rank go up each season even though I don't play ranked?