Why is it considered childish to not marry?

[Stephen]

I hear some people online and in the media talk about those Men choosing to remain single and making fun of them for doing so saying things like Man Up and Marry a woman, or that they have peter pan syndrome.. Why is remaining single considered childish I mean who decides whether getting married or not is the mark of Manhood (adulthood) . Why cant a single man with a successful career or job who has his own house and vehicle among other things not considered an adult by some of these MGTOW shamming artists?