Possible influences:
-Showing your wealth (in the same way as men in some societies show off being able to feed many fat wives)
- The Chinese and Japanese philosophy of your mystic energy (気-ki, or chi in Chinese) being centred on your belly
- Wanting to look like rikishi (sumo wrestlers), the ultimate Japanese men
- Just to make a distinction between the female shape (also in a kimono and with breasts flattened, but with a big obi emphasizing any bumps at the back) and the male shape (obi worn under the belly to emphasize its shape at the front)
- Some kind of cultural universal of manliness that has been lost in the West (see paintings of Henry VIII of England for examples)
