That’s like asking why, if you’re a programmer why you don’t just work for another company on your day off.

NBA players are professionals. They’re paid to play in the NBA season. They get plenty of tailored Xs and Os in their season and post season. They probably all need permission from their teams or stipulations on their contract that they can compete in the off season. If they get hurt, they (and their team) stand to lose millions of dollars.

For players with families and significant ones as well, they’re already away from their families for extended periods.

I’m not trying to be patronising but we do have to think of them as professionals. Not high school ballers who are grateful for any chance to touch the ball. The situation is slightly different for players who are playing for their country or for Olympic pride, etc.