Our entire economic system is built upon this, too. The idea that people other than the ultra wealthy can just retire and... not work when they get old for example (retirement funds are biggest shareholders of publicly traded corporations btw).

Developed countries are seeing the damage of growth stopping and we haven't done much to mitigate it. Productivity per worker is, of course, way up luckily - but so are people's lifestyle expectations. If we all wanted to live like they did in ancient Greek times (minus the pillaging of neighboring countries I guess), we wouldn't even need many workers. But people want so many things that didn't exist 100 years ago, let alone 2+ millennia ago.

For now, we could just solve this by importing more workers from 3rd world countries still experiencing growth. Slow down their economic growth and our decline. But people are racist and don't want to.

The good news is, once those 3rd world countries have strong enough economies, they'll also stop producing babies as retirement plans as has been the case historically (you'd have like 8 or 9 kids so you can live on the family farm while they do all the work - when the economy gets better, you stop doing that).