Because musicians are very shaped by what's gone into their ear. One of the things I'm avid about as a teacher is to get people to listen widely and in a challenging enough way that 30 years down the road, they are not just digging into the same soil all the time. Well, it puts me in contact, in a social way, with other musicians. One of the things I try to teach when I coach chamber music is to get the group to talk to each other diplomatically and productively. Chamber music is one of the most sensitive, tricky things.
People have to be able to collaborate and say things to each other that are difficult to hear.
The history of chamber music is notorious for people exploding and imploding and being unable to live with each other. Yes, all I ever do when I coach my own pieces is try to get people to read the score closely. If it says to play loud, they should play loud. If it says to slow down, slow down. That's something which is remarkably difficult for people to actually do.