Ranked system

I just lost my last placement game in ranked and had won 6 out of 10. When the game was over it said i had been placed in bronze V! I'm not an amazing player but im better than bronze V especially after how right before the reset i spent a month grinding out of it. Why is it I went through all the trouble of playing game after game after game when I can't progress no matter how much time i waste? How is it after all the wins I had in my placement games I was still placed in the bottom tier?