Why women need breasts with nipples is clear - the mother must feed the baby with milk, which comes through the nipples. Men do not feed offspring - so he doesn't need her?
In little boys and girls, the mammary glands look the same. With age, girls under the influence of the hormone estrogen (produced by the ovaries and adrenal glands), the breast develops. In the male body, the hormone estrogen is also present (produced by the adrenal glands), but its amount is not enough for the full development of breast tissue. Excessive development of the mammary glands in men is a pathology, and in medicine it is called gynecomastia. There are many reasons for gynecomastia (more than 30), but the most common is testosterone-estrogen imbalance.
In men, breast tissue functionally protects the heart and lungs from damage. But the heart and lungs are protected by even harder tissue - bone, in the form of ribs.
There are many versions of the presence of breasts with nipples in men - for visual appeal, as an erogenous zone, as a vulnerable spot for a man, and even mythical (we all were once hermaphrodites). In fact, the answer can be found by tracing human embryonic development. Until 8 weeks of intrauterine life, there is no difference between male and female embryos. During this period, all embryos have nipples. After 8 weeks, under the influence of hormones, the embryo begins to develop either female or male, so both sexes have nipples. A similar process is observed in all mammals, including humans.