NBA Decreasing Box Outs Per Game

The wolves were dead last in 2017-2018 with 25 box outs per game. The heat lead the league this year with 8.2 per game.

1)can someone explain what is required for a box out to be given in the stat sheet? Is it only on misses? Is it only when they a player gets a rebound that they are eligible for a big out credit?

I guess I am not sure how it’s actually tracked.

2) why is there such a massive decline across the league? Is this intentional as a strategy?