Placements

I would love to hear some insight from a Riot Employee on this logic:

I play my placements, I got 9-1, all my wins were carries (Most kills, gold, odjs, and dmg, with very few deaths) and i get placed in bronze 5? That make absolutely no kind of sense. I understand that the placements place you in a lower rank then you were last season but how is it that me being bronze 5 last season and performed the way I did get me back to b5? If I was in a low ranking and out performed in my placements I should have been placed much higher...... 9-1 for what?

If you cant get higher than your previous season rank and you are in b5 then why have us play placements in the first place? instead those who do very well should be awarded with a higher start for the season.

Your thoughts and reasoning please.