Earlier quoted context omitted.
Why is the perpetuation of Homo Sapiens a moral imperative?
Why is being nice to others a moral imperative? In fact - why should any decision be based off morals? The continuation and survival of the human race is the top priority among a large population of people. Some contribute by researching new medicines (Why do this?), others improve quality of life for others (Why do this?), others have children (Why do this?), and others look for a way to get us away from a potential…
The goal of colonizing another planet would give a small subset of people the ability to continue living if the people on Earth were to destroy themselves. This is a hypothetical situation that -if it happens- will kill off almost everyone, dragging hopes, dreams, money, infrastructure, standards of living (basically everything that makes life enjoyable) with it. So if that is destroyed, why does it matter if humans continue living as a species? Especially on an extremely harsh planet.
Your analogous examples differ because all of those things -medicine, quality of life, children, even sustaining our environment- help us now. We do those things to make our own lives longer, improve our own children's lives, and make our quality of life greater, not some hypothetical future civilization away from Earth. You're right that humanity's best interest is survival, but I think way more people are concerned with their own survival and I think that's where the true incentives for those examples lie.