In a lot of cases I wouldn't be surprised if it was for legal reasons. It could be a case of somebody or some corporation holding the rights to that name combined with their image. To make things simpler and avoid any battles they might just decide to go with something else. Another reason I think things like that could happen is that somebody they have worked for in the past has pissed them off but they are still making money off of their previous work, so to spite them they could try to change their name so there is less of a possibility they will help them out in any way to bring in customers or cash to somebody they had a falling out with. If people used a search engine on their old name they might go to sites they have worked with in the past and that would help the people they don't like anymore. Also, it could very well be they just want to start fresh and change their image. I do find it irritating how they change their names all the time though.