I'm not being snarky (at least not intentionally). But you're saying a thing that is at the very least a superpower-level goal, if not a civilization-level goal, that is very clearly not a current priority, should. What's more you're saying it in a way as if it's completely self-evident that we should change our global priorities to focus on this without the slightest evidence supporting that assertion.
Well where do you see humanity in the future? In a realistic but also optimistic future? To me all of these futures involves us being a multiplanetary species, and starting to expand out into the cosmos more broadly. It's not only the only way we'll ever become a post-scarcity species, but also the only way we can secure our own survival as a species. There have been countless mass extinction events on Earth, and we're well overdue for another one, and it will come.
You're also probably grossly overestimating the cost. The SpaceX Starship program has been privately funded on a budget of ~$2 billion a year including all costs - research and development, construction, launches, etc. And once built it's expected to revolutionize space (again) sending launch costs to less than $10 million per flight, and price per pound to space into the low dollars! And once we can start transiting massive amounts of cargo to Mars, at a very affordable cost, colonization is very much within the domain of possibilities.
I would not contrast prices against NASA. NASA is largely used as a tool for pork and graft by Congress, that occasionally launches something. Their latest ship, the SLS [1], is literally reusing Space Shuttle era tech. I mean literally - the SLS is reusing refurbished Space Shuttle RS-25D engines, solid rocket boosters, and more. Managing to spend tens of billions of dollars over 13 years (and counting) to develop this is the special sort of talent you can only get from a company like Boeing.
So colonization will be costly, but it's nothing like a civilizational goal. It's just that our civilization only has governments mostly interested in fighting and dominating one another, just as has been the case for the entirety of human civilization. So we never really get to see what we could actually achieve if we tried. But what's finally changed is that these sort of grand achievements no longer require governments. Costs are plummeting at the same time private capital has skyrocketed. So the future looks brighter than ever!
You could reasonably define "post-scarcity" as "we've got more supply than we need".
In this regard, you can define scarcity and post-scarcity independently for every consumed resource.
We've been post-scarcity for oxygen since before we evolved; post-scarcity for water in most of the settled world; and now? Now we're post-scarcity for biros, photocopier paper, USB cables and wall-warts, and tchotchkes.
The only reason we're not post-scarcity for intellectual property is that we've created rules to induce artificial scarcity.
>We've been post-scarcity for oxygen since before we evolved
Have we? Our supply has been getting tainted with worrying levels of trace contaminants. If we had 100x as much atmosphere, maybe that wouldn't be an issue yet.
>post-scarcity for water in most of the settled world
"""Globally, 2 billion people (26% of the population) do not have safe drinking water and 3.6 billion (46%) lack access to safely managed sanitation,"""
As you quoted me, most of the settled world. Most. As in, more than 50%.
I'm not being snarky (at least not intentionally). But you're saying a thing that is at the very least a superpower-level goal, if not a civilization-level goal, that is very clearly not a current priority, should. What's more you're saying it in a way as if it's completely self-evident that we should change our global priorities to focus on this without the slightest evidence supporting that assertion.