Ayu Voice & Ayu Instrumentals

[mellody]

I'm sorry if this was posted before, but i want to know your opinions..

About Ayu Instrumentals, why Ayu backing voice is still appears?
Another artist with the same label, i mean Avex, like Ai Otsuka,
are having clear instrumental, but why Ayu is like that??

Sometimes, when i hear Ayu instrumental with her backing vocal seems annoying for me..
And then, in her making of, the instrumental were pure!!
Why Ayu doesn't add the clear version of her songs in her instrumental?

Is it because, her voice doesn't really good to hear?
For me Ayu voice was very good, even without that backing vocal..

Anyone can explain or give opinion?