Everyone needs to know what you're doing, who you associate with, what movies and TV you see, whether you plan on extended schooling, what you do on weekends, etc.
They want you to account to them. If they believe you're acting not quite in accord with their standards, they'll inquire about your business.
The elders believe they are literally, God's gift to everyone else. They expect total openess in every matter including your love life, your goals and your secrets.
Like I said, Witnesses are so (too) nosy.