The thing is with a boycott, Sunderland and every other club does it by not attending your clubs games if your not happy with the team or the way the clubs ran. That is showing discontent and telling the club that until things change you are not coming back.
Newcastle get the media attention because they jump up and down and tell the whole world they are not going to the games because they are complete and utter gobshites with a monumental size chip on thier shoulder
This isn't an organic abstaining from games due to poor performance, it's been a co-ordinated effort with a common reason behind it.
If it was like every other club, how do you explaining our average attendance actually going up after we were relegated?