Is the "same old sound" the real reason of Ayu's declining sales?

[Cahz-]

Whenever there is a conversation of international jpopers / fans about Ayu declining sales, the "same old sound" factor is one of the most mentioned.
That she makes the same boring ballads, recycle sounds, every album is like the prior one, etc.
But all the japanese comments I've red all through the years about Ayu's sales, the following things are mentioned:

· She was cute on her prime and now not anymore
· She has turned into a joke
· She turned into a diva
· Her voice is not so high pitched like before (this one I read it when Love songs was released)
· She can't sing anymore

Not one single time I've red japanese comments about the sound of her albums.
So, what is the truth?