Why is it so common for men to develop gynecomastia?

B/c: Hormonal & weight changes are common as is the use of causative substances.

Look x causes: Obesity, medications for prostate, other medicines like spironolactone, liver disease like cirrhosis, lack of testosterone (andropause), intake of estrogen, and who knows if high content of estrogen in certain food? In young adolescent males is common to have first unilateral gynecomastias due to hormonal changes.

Hormones: All men have rudimentary breast tissue (small amount) and an imbalance of testosterone and estrogen can make this tissue grow. It's common in young men starting puberty, particularly if they are heavy, because there's a higher level of estrogen associated with excess fat.