I think just a stylistic choice. Honestly, the only reason it bothers me is that the people who aren't fans of Transformers (so basically most people on this planet) will start throwing around "BumbleBee" as the proper spelling of his name. I mean, I get that ultimately it doesn't matter but I know myself and I know it will bother the hell out of me.
Well clearly they retconned his singular name into a first and last name now. Bumble Bee. Mr. Bee if you're nasty.