I've got it pretty good, and I've voluntarily decided to not reproduce.

And just in case you wanted data rather than anecdote:

https://ourworldindata.org/grapher/children-per-woman-fertil...

Your world view is somewhat upside down!

Then why have birthrates fallen across almost the entire world as the economy has gotten better?

Real world fact is opposite tho, not some "bad things", in poor parts of Africa they produce more, only in hedonism lover places they stopped producing, its people thinking for themselves, not a bad thing. It's not about economy.

All poor people everywhere have more kids even today.

> Do you know how bad things have to be, for a mammal to voluntarily decide not to reproduce?

Actually, the famous 'Mouse Utopia' experiment (Universe 25) arguably showed the exact opposite. The population collapsed despite abundance of food and water without any economic hardship.