Why do many jazz pianists like to talk while they're playing, especially live with a backing group?

On many jazz recordings I hear by the great classic jazz pianists, they're talking while they're playing, not really trying to be heard by the audience. It's more like they're talking to themselves, like it helps them get "into the music." What's this all about? Are they just "being cool"? Or is it a trendy thing that they started doing, because one artist did it and they ALL wanted to imitate him?|||I don't know about "talking" but I've certainly heard jazz pianists making vocal noise as they play, this seems to be a reflex when they get really into the music. This is the same effect when drummers or guitar players make goofy faces when they get really into the music. Trust me, if I didn't have a trumpet to my face I'd be doing the same thing.|||It's not just piano players, I've seen bass players and guitarists do the same thing. A lot of the time they are "singing" what they are playing, although they can't really sing.|||They are enjoying their Hi-tension mood naturally.