Probably just wants to keep medical stuff as private as he can. Once you open the can of worms by answering 1 question perhaps the thought is that will only result in more invasive questions.
Either way, if you've seen him with no shirt/jersey on you can see a visible scar just below his right clavicle which would indicate a surgery was performed. The
podcast taping he did with Kevin Hart in June at the Fanatics event in NYC was when I noticed the scar.