Board Thread:Character Discussion/@comment-3574574-20171103160130/@comment-25926288-20171103165749

He probably casted the curse. As we know it's probably not a Dark Curse, the heart isn't a necessary requirement (plus Fiona casted it with a ball of black fairy dust).

Or it could be that they didn't want to change is name, lol. To be fair, Regina nor Fiona changed their name when they casted the curse.