Societal norm in the U.S.: "Everyone" has a circumcised penis
Ethnic, cultural or religious reasons, e.g., Jews, Muslims, some Christians
Identification with other males, e.g., father, brother
Easy hygiene (no need to retract prepuce for cleaning in older boys and men). This is a common belief in U.S.
"Prevention": Less risk and ease of neonatal circumcision compared to a desired or necessary one in later life (anesthesia risks increase, more pain and greater healing time outside of newborn period)
Perceived medical or health benefit: Less preputial problems, less penile cancer, fewer UTIs, fewer STDs
Personal preference of appearance