Because Mario once got a hamburger at McDonaldds, saw the sesame seeds and said, "These are-a good seeds says-a-me!" The guy at the drive-thru window laughed so hard that Mario said "says-a-me" (which sounded like sesame) that he told the press, and it became a huge thing. Naturally, everyone loved MArio and decided that sesame seeds must be very special if Mario, the hero of Mushroom Kingdom, thinks so. THey even tried to get Mario to be the new 'Sesame Seed Boy' but it didn't work. Mario just like sesame seeds, and didn't want it to become a huge thing. He couldn't help it if he has an italian accent and says "says-a me" which sounds like sesame. Mario doesn't buy at McDonalds from this point on. And that my friends, is the story of why sesame seeds are more popular than any other seed...
Is Waluigi happy with his name?