Gordon Hayward is making $31M in 2017 with the Celtics; breaks his leg on opening night.

So in the end he plays half of one quarter of one game. And the Celtics that season played 101 games. So prorating his salary out to the time he was healthy, Gordon Hayward gets $38k for that year.

Which A) sucks for Gordon Hayward, but B) also sucks for the Boston Celtics. Suddenly they're under the salary floor and need to find a way to spend $30M with no quality free agents left. But they can't take on any long-term salary either because Hayward's salary will be back on the books next season.

And of course, other teams aren't worried about shedding salary since they know they'll likely have their own salary drops when players get hurt. And if they don't they can choose to sit someone who is dinged up and use that as a cost-saving measure.

Beyond that it would also become a matter to help recruit players - if Team A will call you injured and not let you collect, but Team B will have you dress and 'available' even with no intention of getting off the bench, then free agents are going to go to the team that isn't anal about enforcing this.