I think this underestimates our most primal of instincts, survival. Those people who died at 48 a century ago had no less want or determination to live longer, than did those who die today at 78. In those times, their options were extremely limited, so as a culture, our norms prepared them better to accept death. Nowadays we have many options, and modern medicine has become the ultimate tool of our survival. Yet another profound ability that separates us from other animals.