Because wretched nigh on universal poverty, above 50% infant mortality, famine every 20 years killing perhaps a quarter of the pain, endless toil, all these things are bad. Given the choice between living like the average peasant in 1800 and maintaining something like our current first world standard of living and health while so destroying the environment that the first planet we need to terraform is Earth people will choose the latter. Most of the world’s population was peasants in 1900. No one had antibiotics. Air conditioning was practically unknown.

The state of nature is hellish and people will absolutely pave everything while breathing air that tastes like an ashtray to avoid it.