Your third choice, "there isn’t one answer that remains the same for everyone all the time" seems most true. After all if there is a constant, it's Change: We all age -- people, animals on surface, in air, under water. Even rocks and rivers, the climate.
But I guess you are concerned with HB, the old ones like me, an Octogen. Why do they remain stuck in ways that may be incompatible to the present, is what you're interested in? Because we also get comfortable with ways that we have lived in -- with places, routines, possessions, culture, climate ....
So HBs (and perhaps animals we share space With us they too begin to change) -- in ways that still obey the more fundamental 'laws of nature' such as survival. But here humans also differ: we sometimes give our life-on-earth for promises in better or more worthwhile life hereafter. Remember that mass suicide in that small country on the northern edge of South america where they committed mass suicide? Or brides who used to jump in fire to die if their husbands had died -- now outlawed in India, or foot binding that was practiced in China, or long-necks in North of India -- but changed?

So why change happens is equally more fascinating for me. The China 'miracle' that iss going head to head with the Most Powerful nation on earth all within a few generation -- including at what cost to human life -- is a ripping phenomenon for me.

Thankfully we all are given 24 hours each day as we wake up -- with No Conditions Attached. HOW we spend it is fist and foremost my business, unless of course where it may interfere with people around me. So if I want to die like a Socrates, among friends drinking my hemlock to end MY life because it is no longer as ''interesting'-to-me' and I've made sure I've paid my loans (chicken in case of Socrates) the I and my friends should be able to do it.
I hope we all have friends who are with us when we may need them most -- one thing that is Outside of HB's control. Because friendship is MUTUAL.