Why does Tuck look at the unconscious stranger with envy?

The stranger in question is the man in the yellow suit. He's unconscious because Mae Tuck's just whacked him over the head with a rifle butt after he tried to kidnap Winnie. The irony here is that it's the Tucks who are supposed to have kidnapped the little girl. But this wasn't the case at all; it was nothing more than a cynical ruse by the man in the yellow suit to get his greedy hands on the Tucks' spring of everlasting youth.
As he lies there, unconscious from his injuries, it may not seem that anyone in their right mind would envy the man in the yellow suit's situation. Yet that is precisely what Pa Tuck does. As Pa stares at the stricken stranger, Winnie notices an unmistakable look of envy on his face. Pa, like the rest of his family, is immortal, and immortality can be a bit of a pain for him at times, so much so that he often wishes he could die. That's why he's so envious of the man in the yellow suit as he hovers between life and death; he wishes he could change places with him.