I'd be interested to see the same poll done in Japan. In the US, the culture favors the young, the athletic and the productive. In Japan, at least historically before they were affected by western culture, the Japanese revered their elders' knowledge, experience and wisdom.
If you live in a culture where people are respecting you for your age, it's easier to want to live longer. Some of the oldest people in the world are in Japan.
It's not a mystery to me why Americans don't want to live longer. It's more of a mystery to me why Americans don't want to change their disposable culture.