The fate of a female J-pop singer.
Boa sings well, but I think she is trying to imitate Britney Spears. And since Britney Spears lately has gone wild, it is natural for Boa to adopt a sexier image.
In East Asia, being too young is not as much as a problem as being too old. Usually, it's the younger the better. It is a trend Boa alone cannot fight off. But if she could compose, then she would have more control.
Look at Namie Amuro... Of course, Boa is more popular than her in recent years. Boa is a star (high growth, high market share) while Namie Amuro is a cash cow (low growth, high market share) heading into a dog (low growth, diminishing market share) in the product life cycle. Most composers would hand in their good songs to Boa. It's such a vicious cycle.
P.S. I prefer Namie Amuro, but recently they didn't give her a lot of good songs to sing. And who can blame those composers? Giving their best songs to Boa is like a sure-win!