Why Does All Jazz Sound The Same?

Yeah, I know.  I was mocking my coworker who always says that jazz all sounds the same.  I should have explained that but I wasn't very much awake yet when I had that thought.  
I told him he should try listening to the Grateful Dead (who I love BTW).  A lot of people say that all Dead music sounds the same.

@snackeyp What you are hearing is related to musical training. Classically trained musicians know where the right notes are and get them on the first try, while Jazz musicians go by trial and error. Jazz bass or guitar player "walks" all over the fretboard until he finds the right note. That makes all Jazz sound very alike, no matter who plays.

Hey, I think all Baroque sounds the same. Tinkle, tinkle, tinkle jing.

@kijanki, 
I don't know if your comment is tongue in cheek or not. If your serious see my post above. Those musicians sound nothing alike playing the same songs. Very different approaches and improvisations. Probably you are posting in the same spirit of @snackeyp. 
Charles 

@charles1dad   That was a joke