Personally I think guys are playing TOO MUCH in the offseason. Nothing wrong with staying in shape or doing drills but the body needs rest. Then people say well how does a player get better? I coach AAU and rarely do we play full court. I have everyone doing drills that they need to work on. Kids play too many games and never work on their games. Some don't know how to make post entry passes, post moves, anticipate passing lanes, help defense, etc.
You get better by working on individual drills or 2 on 2 but full court games and summer league is too much. 2 on 2 you can work on pick and roll, shooting, dribble, drive, man defense, post up...but you aren't running up and down the court. This is why you didn't have all these injuries back in the day and these days they have better travel, personal trainers, chefs, better equipment, better shoes and the game is less physical.
The only answer is to rest in the offseason and keep your body fresh for the season. Just my opinion.