Based upon personal experience of being born and living all my life in the U.S. and from what I've gathered second-hand about other cultures, you are correct about men (at least straight men) being less likely to display what could be considered affectionate behavior towards each other here.
Why this is so in a general sense I couldn't tell you for sure, other than I likely think it's part not wanting to be seen doing anything homoerotic or "feminine" and part the cultural history of this country that portray men as rugged and independent, which means not showing emotional vulnerability.
For myself, I've just never been a touchy-feely and huggy type of person and am very choosy with my affection, even towards females. My wife is one of the few I can let my guard down with and almost all affectionate embraces with other males have been limited to family members and a rare few friends that were either in dire emotional straits and needed a hug or having gone through a significant event together such as when I was in the military.
Maybe part of this being averse to touch is just me being me and the result of not being around or growing up with mega-affection and part of a holdover from some of the jobs and situations I've been in where not letting anyone get physically close or in your space was a matter of survival.
But either way, the fact anyone, regardless of gender, may not want to be more openly affectionate or have more physical contact with me is an advantage, not a lament.
