Can see the logic in making a month the length of a menstrual cycle (give or take a bit) or indeed a lunar cycle (give or take a bit). It's the "give or take a bit", bit that makes it so odd.
We seem to have had a propensity for the number 12 over the millenia (months, hours, inches, peenies in old shilling, eggs, to name a few that spring to mind) - can't remember the reason why.
Indeed, even the months seem to be numbered wrongly - the ninth one is Sept, tenth one is Oct, the ninth being Nov and the twelfth being Dec.