The battlegroup theory was debunked as I found players outside my BG around.
The problem with the CRZs is not only is there no control but 1. There is no way to know if you zoned out of your realm and into another realm and 2. If you do, which realm you are on. Zoning and and out only occurs when you a. cross a zone border or 2. taxi-mount.
Problem is if you use a taxi mount and see a rare spawn where you are going to land, you could zone into another realm when you land and it won't be there when you go back because the realm you saw it on was your own realm on the taxi-mount and you zoned into another realm.