I think it had to do with his name being Eggman in the Japanese versions of the old games and them just deciding to use the same name everywhere, maybe it just made things easier with any texture work that would have his name or something. I prefer Robotnik as well though.
Gees Knuckles got friggin BEEFED... Perhaps it's tape on their shoes, he runs so fast he has to tape his shoes to his legs xD I still don't get why they decided to rename Dr. Robotnik to Dr. Eggman...