Let's figure out what this cycle is. The ovarian-menstrual cycle (aka the menstrual cycle) is a cyclically repeating change in a woman's body, which is based on the ability to conceive offspring. The cycle begins at adolescence 13-15 years and ends at 50-52 years, and lasts an average of 28-30 days. During this time frame, a woman has a chance of getting pregnant every month. Thus, monthly recurring cyclical changes in a woman's body provide a conscious choice of conception, regardless of the season, moon phase, weather and climatic conditions, which contributed to a great push for evolution. And also made it possible to enjoy intercourse, and not only reproduce the future generation.
Very simple - reproduction.
The reproductive cell in a woman's body is created for some time. Then she waits for sperm to come to her for fertilization. A cage cannot wait forever, it grows old, keeping such a cage is unprofitable and useless, and it dies. At this moment, women also have menstruation. And then the reproductive cell in the woman's body is created for some time ... well, you understand, everything repeats.