Noted as you said, up here in Queensland, Joybell.

I think it had something to do with the pronunciation - originally Moll - with emphasis on the final 'll' and a short vowel to now be nearer 'MoWl' - emphasis shifted earlier onto a longer and stronger vowel.

It was happening earlier, but the comedy show - which I think just picked up on the shifting trend, definitely accelerated it to become 'cool'. Of course do not forget the MALE 'Adrian Mole' book which predated the female comedy show.