The goal of life is whatever each individual has decided the goal of life is. You may not get why someone might want to live forever, but that doesn't invalidate that desire; it just makes you unable to see their point of view. That's ok, though!

I think 100 years is far too short to experience everything our world has to offer. I get that motivation could be an issue for some, but a motivated individual would certainly appreciate extra time to broaden their experiences!