しかし、許可をもらわないでコピーした漫画をインターネットで読む人が増えているため、漫画全部の売り上げは少なくなっています。
However, because the number of people who read manga on the internet – that has been copied without permission – is increasing, total manga sales are decreasing.
No problem with understanding (I hope), but 漫画全部の売り上げ looks weird to me. I feel it ought to be 漫画の全部の売り上げ. Is this a typo? If not, why is it okay to write it like this?