Jada has alopecia which allegedly causes hair loss. (I say 'allegedly' because I'm not looking it up, am not a doctor, and don't care if that's true).
If you think a woman gaining weight is emotionally traumatic, one losing her hair is devastating. Whatever Will and Jada's past, Rock would have touched a major nerve with a couple where the woman is dealing with hair loss.
Will's delayed reaction, the laughter...c'mon man. No one's been so shocked by something they didn't laugh at first, a sort of nervous chuckle as their brain processed WTF just happened? No one here has paused to take stock of something major and out of the blue? Putting myself in Will's position, I don't think his response is unusual.
With that said, a slap like that is a good effort. It is demeaning to the one slapped...you don't think enough of them to throw a punch. Counterpoint: if I might take a charge for battery on a fellow entertainer, potentially ruining my rep and future in that field, after a comment that likely traumatized my wife (degraded internationally and live in front of her peers)... a motherfucker has to hit the floor. "This is the way."
Will's tearful apology afterwards...weak, but whatever. Own the moment. Go full Nathan Jessup.
Awards shows and Hollywood are a joke anyway. Now future hosts will "uber-vanilla" their monologues to avoid this sort of altercation. This incident could without exaggeration be one of the last "wow" moments in the Oscars' history as viewership declines and people lose interest.