In the Netherlands we don't really have a big NIMBY issue and we still can't keep up supply with demand. Supply is complicated and not just restricted by zoning. One key thing to understand is that private companies build homes, not governments. And if it's not profitable to do so, it will simply stop. And if not at least 75% of the project is sold beforehand, the project is stopped altogether. And this is how our go…
> There's an economic downturn and the building of new homes slows down or stops. This happened over here from 2008-2014 creating a massive backlog, in turn leading to a pricing boom in recent years. Ideally, you'd keep building during a downturn but nobody knows how as there's no buyers and it's too big to subsidize.
If the return of demand was predictable then deep-pocketed investors could have kept the building running and made a big profit. Why didn't they? In my experience this is usually down to overregulation one way or another, either rules that make it too hard to invest in housing or because rules that make new homes a lot more expensive than existing ones (e.g. you mentioned energy rules, accessibility requirements, that sort of thing).
If the return of demand wasn't predictable, then stopping building was arguably the correct move.
> Surely the entire western world would not have this problem if it was a simple as a policy change.
The correct policy change is known but counterintuitive and unpopular. (And for many of the voting public it's not seen as a problem; they benefit from rising house prices, so who cares about the young people being priced out?)