This confuses me, Laporte should easily be 3rd choice, brilliant defender for his age, really special talent.
It's not confusing, we are talking about a national team not a club. Sakho is a good teammate, he creates a good locker room atmosphere and he is decent with France. There is no benefits to choose Laporte because he won't play like Sakho isn't supposed to play.
But don't be fooled if Koscielny or Varane are injured, Laporte will most likely jump Sakho and Mangala.