My best guess is because you registered for this forum way before any of us. The tag lines may be added by their computer as new people register for the forum. I'll bet if you re-register you could get one.
My second guess is that "they" can't think of something to top Pooh-Bah!
I would say it's because you and Erin are so "old" [members that it] you're special and don't need a tag. Prolly you are original members and us "Johnny-come-latelys" need something to identify us. We love you both even if you are "old!"
Don't wait too long to tell someone you love them.
Very Very strange I was just going to say having nothing under there is probadly better then "stranger" because that's what under my name but I just noticed I have moved to "newbie" It sure sounds better then the other.