Why do men have nipples?
If female mammals have mammary glands, then why do male mammals also have similar mammary glands? Do all males have them and why bother having them at all if they don’t do anything?
It's an evolutionary thing. If you look at how we develop in utero, for the first few weeks male and female babies look absolutely identical. It's only subsequently that you start, under the power of the hormones pumped out, to change and alter your anatomy. But because you develop a lot of these surface structures and appearances when you're very early on in development, you've got them whether you need them or not. There is one example that I've managed to find that's a male and uses it's breasts to potentially breast feed as they certainly lactate. That's a Dayak fruit bat and they live in Indonesia. The male produces about a tenth of the amount of milk that the female does.