Why doesn't Atlanta pick Schwarz if he drops? He is suppose to be what? A top 10 prospect or something? Or why doesn't a team like Calgary pick a player like Green or Valabik if they drop?
Calgary will take a Green or Valabik if they drop because it gives them room to trade a d-man for the scoring winger they truly need, one that can step in sooner rather then later.
Atlanta may pick Schwarz at #10 if the guys they want are gone because they can trade him for their needs.
That's what the BPA theory is, take him and then if you don't fill a hole with him you can trade to fill a hole. You never know, somebody could get a career ending injury or you could pull a blockbuster trade and your needs instantly change.
Same reason why Minnesota doesn't need a goaltender. Doesn't fit their needs and while it might be a top 18 player, not the BPA...
"Needs" and "BPA" are mutually exclusive. If a goaltender is the highest player on their list come their pick then he's the "best player available". If you start factoring in needs then it's no longer the BPA.