As others have said, because it's a key military capability.

Humanity is what humanity is, not what we wish it'd be, so key military capabilities need to be developed or you get razed by the guy who did develop them. Doubly so now that we've rediscovered that culture is much more resilient than we'd thought, and that different people want Earth to look in different ways.

Do we all wish we'd stop ecological collapse instead? Yeah. But it's not going to happen so it's irrelevant.