Other than tides, why do you need to know when the next full moon is? And can’t you just look at the moon and see how close it is waning to the full moon?
Not saying the calendar is definitely a woman’s, but wanting to know when you’re going to start leaking blood onto everything near you seems like a good reason to track a period. Plenty of women are regular like clockwork, I was at 26 days almost exactly for years.