The use of the term has great power to control. I recall sitting at a meal with some other JWs and daring to propose a line of thought that was rather liberal, though still a reasonable interpretation of the Bible. A jumped-up young "elder" at the meal glared at me and said, "That sounds like apostasy, brother." It was a sharp reminder that I was part of the Club and I'd damned well better follow the line.
It used to rankle me no end when, sitting at the weekly Bible Study meetings at someone's house, the conductor would be chatting with everyone using their first names, then he'd call the meeting to order and say, "Brother X, can you read tonight and Brother Y, can you open with prayer?" As if God wasn't watching until we switched to Brother and Sister.
Yes, it's all about control.