- A political unwillingness to reign in private capital that's exacerbating resident housing shortages / rent increases (read: AirBnb)
- An infrastructure underinvestment in building sufficient new housing (or motivating current housing owners to densify)
- An underappreciation (Germany) that one can't switch energy mix at nation-scale without first building replacement capacity
- (Europe at least has far more child-rearing-friendly policies than the US)
But all of that is a "maintain demographic shape AND ___" problem.
Countries with inverted demographic pyramids go financially south very quickly.
At best, there are some extremely hard compromises to make (higher taxes on a smaller working base, or decreased social/retirement benefits).
At worst, there are no solutions to balancing a budget and things spiral out of control quickly.
It's underappreciated that "young immigrant labor is funding the country".
There are other solutions, e.g. that the wealthy boomers pay with their houses for their retirements or are forced to rent out their huge properties.
The retirement ponzi scheme needs to stop at some point anyway. With automation one might also need fewer workers.
Most importantly, many immigrants receive social security and are not employed.