Something strange happens when people get wealthy and advanced enough. Cost of living rises, workload increases, it becomes unaffordable to have kids. 30 years later, everything is empty.
Places like Australia have plenty of land but, nah, everyone wants to live urban where housing prices are insane or inherited.
Food costs often go down in developed countries, cheaper than developing ones. Maybe they're so low that they can't afford to become farmers anymore? Not enough people buy corn and corn price is so cheap that it gets made into HFCS. But if you can't mass produce cheap corn, you're screwed and get a desk job.
So we have the service economy. Everyone sells services to one another, works from home, makes tons of money. Madrid has top-tier designers, chefs, doctors, moneylenders, nearly every kind of service. All the piles of money in a concentrated place like Madrid makes the whole place overpriced. If you happen to be the best tuna butcher in Western Europe, there's a limited number of places you can work, but many of these specialist jobs are also wfh.
Is there a hack to this though? Can our top tier Spanish pixel artist sell her services to someone in suburban Canada?