If you're a young guy and you honestly question why a man would ever get married then you don't need an answer....the question is rhetorical.
There's nothing wrong with being single with no kids, but remember that perspectives do change when the novelty of the bachelor lifestyle wears off. At some point most guys' chiseled, good looks from their youth begins to fade and is replaced with receding hairlines, beer guts and love handles. I'd rather become ugly with someone than just become ugly and be alone LOL. And spare me the bravado of "I'll never change how I feel and I'll always be chiseled and handsome." Things change, perspectives change, desires change. Certainly some men are happy and content remaining single from their 20s to the grave, but most often things change because lives filled with superficiality and pretentious nonsense quickly becomes lackluster. When you're married to your best friend you have something real and when you make a family with that person it makes it that much better. Make no mistake, marriage is work and struggle at times, but it's also wonderful and empowering if you're with the right person for the right reasons. In those instances the struggles often don't matter.