Stability is generally rewarded - sudden drastic changes to a primary parent's living situation, religion, employment, etc. is not seen as great for children. A

Stability is generally rewarded - sudden drastic changes to a primary parent's living situation, religion, employment, etc. is not seen as great for children. Also, sudden shifts in behaviour can happen because of serious mental illness (not saying that's true here), which courts would understandably be worried about. If a family was mostly happy, healthy, and stable, and one parent decided to leave the family and make drastic changes (to a new religion/community/city/whatever), the safe thing would probably be to leave the kids with the piece of the family that hasn't drastically changed. Most of the time, anyway.