He's not saying anything of the kind. Maybe you should read the article again.
So, what is wrong with praying for his death? For relief from his manifest sufferings? And for the opportunity to pay honor to his legacy by turning to the responsibility of electing a successor to get on with John Paul's work?
It's called sanctity of life - even that of the crippled and suffering. There's zero evidence that the pope is senile. If the pope is comfortable with having the will to live and continue his work in spite of his sufferings, why is everyone else so UN-comfortable with it?