It might be the ultimate endeavor. Right now we live in relative scarcity, so resource gathering dominate our culture. But imagine a thousand years from now when robots produce everything, and material is plenty. What do we do then? What's our purpose as a species? A good candidate is striving to maximise healthy and dignified earthly life across the universe.
History shows that whatever our “purpose as a species” is, those with more power will want to take more from those without. This is incompatible with “maximis[ing] healthy and dignified earthly life” for most of the population. And there is nothing to be optimistic about; this won’t change in a century or a millenium.
A nice video that goes in depth about how people just don't have an intuition about exponential growth: https://www.youtube.com/watch?v=LqcHG7QUK9k
Of course it is true that in a finite universe, exponential growth can only continue for a finite amount of time.
But that time could easily be far longer than you or I will live to see. We could be centuries, millennia, maybe even millions of years, away from the peak.
The peak of human civilisation might be the point at which every inhabitable (or feasibly terraformable) planet in the galaxy has been colonised. (That assumes that intergalactic travel will never be feasible – an assumption which is probably true, but we can't be certain about it.) Peak galactic colonisation could easily be several million years hence–if we ever get there. Of course, we could quite easily annihilate ourselves a whole lot sooner than that, or interstellar colonisation could turn out to be permanently technologically or economically infeasible, or a bunch of other possibilities. But that's the thing, nobody knows where the peak is, worst case scenario is we could be living in it right now, best case scenario is it could be millions of years into the future, and lots of possibilities in between those two extremes.
Also, aesthetic.
Also, reduced chance of extinction (before each given point in time).
I am simply talking about when humanity reaches peak exponential growth. Staying on the one planet, it has to happen a lot sooner than if we colonise other planets in the solar system and then go on to colonise other star systems as well. With galactic colonisation, the peak could easily be millions of years away. Without it, the peak has to be a lot sooner than that.