Why is Dr... Eggman called Dr... Eggman when his real name is Dr... Robotnik

The character of Robotnik/Eggman was created by SEGA in 1990. When the character was shipped over to the U.S along with the first Sonic game in 1991, SEGA of America decided to officially make his name Dr. Ivo Robotnik, because it sounds better. He stayed Dr. Eggman in Japan. By 1998, SEGA had decided to revert his name to Dr. Ivo "Eggman" Robotnik worldwide, for unknown reasons.