Why do Mums seem to be less mood balanced than Dads? Is it experience or habituation?

Bringing up a child is no child's game especially in country like India where the mother is solely responsible for child care. Its a huge responsibility and warrants great amount of skill, patience and has its own falls. Mother go through it 24*7 whereas fathers on the other hand typically is responsible for child's actions after office hours and that too he shares the dice with the mother. so while he enjoys team work the mother labors solely. this is bound to put her off balance and hence the fluctuations in mood. It's all about sharing the load according to me.