"Why occupy a public space and impose your noise on other people?"

You could also say that to football enthusiasts who roar and shout at TV screens in the pub, noisy domino players, those who play music you don't like on the juke box etc, even those who like to converse loudly...

They are called public houses. So, presumably all members of the public are entitled to use them, within reason, for drinking and socialising... even musicians?
Not necessarily all at the same time, of course, and everyone should show each other a bit of respect just as you would do when visiting a private house.