^ your right, song writers make alot of money from singles and albums sales so as Ayu writes her own songs that would contribute to a much larger chunk of the $$$ earned from sales.
I know song writer Cathy Dennis still makes lots of money from the songs Can't get you out of my head and Toxic as she wrote the songs and I think owns the rights to them so if the songs are used anywhere like adverts she would get paid as well as the singers and producers etc etc.
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