Because eventually there will be an asteroid or nearby supernova that will destroy civilization unless humanity’s total wealth and technology have improved vastly between now and then. Stasis is death.

I don't find it likely that my kids or grandkids will have better odds of avoiding asteroid or supernova death by working to death to try to become interplanetary ASAP.

I think doing so would introduce far more risks to them. Space ain't friendly.

Beyond that I find it hard to care to drive anyone to work their ass off today for whatever humans are around 100+ years in the future. And, of course, more technological development brings more chance of mass self-inflicted die-off of humanity anyway. In 1900 it would've been much harder to kill 10%, 20%, 50%, 90% of the global population than it is today.

Everything is death eventually. And predicting the future is hard.