Dubs are often adapted to the American culture. I often have some problems with Japanese voices, mainly men voices. Maybe it's a question of habit. I just like well done American voices. And surely, if we want anime to expand in America, it's something that could be important for the average guy who's not used to Japanese voices.
Dubs are cheaper.
A dollar saved is a dollar you can put on another anime tape. Actually, dubbed songs. Not only these are far from being as good as the original ones, but they are sometimes childish. And if I was the writer I wouldn't be too proud. I know the show is mainly aimed at young girls, but I think such childish songs are somewhat an insult to their intelligence.