[Fom]

I think Britney released Circus because being in the limelight is all she knows and being busy is what makes her feel happiest. In all fairness she only went crazy when she wasn't working.
She has been loved and adored by millions of people all of her life, to take her away from that probably makes her unhappy, it seems weird to us but none of us have been famous since being about 9. So we wouldn't understand.