Like most human related things there is no single cause.
I can't comment on Iceland.
However, South Korea has one of the most crushing work cultures in the world, with insane work hours. Most people are not even in a relationship yet alone with kids.
In Portugal you have a huge problem of disposable income. Median salaries are insanely low and stagnant when adjusted to COL. To the point that by now most former 'Iron Curtain' EU members have surpassed Portugal in workers income both adjusted and absolute.
The fact is, when comparing across all countries in the world, that the harsher the conditions, the more kids there were. Do people really believe that their ancestors lived in better times for raising children than currently? It is precisely because they didn't that they had so many, as they needed labor for agriculture or to make sure at least a few survived since so many would die before the age of 5.
Now, I am not having children either, but I will not deny that even in the best of countries, when controlling for all of these factors, people still aren't having children simply because they have no want or need of having them. That's it, that's the reality. Now it is an uncomfortable truth for many, but many people nowadays, me included, just don't want them, for no particular reason at all.
I can't comment on Iceland.
However, South Korea has one of the most crushing work cultures in the world, with insane work hours. Most people are not even in a relationship yet alone with kids.
In Portugal you have a huge problem of disposable income. Median salaries are insanely low and stagnant when adjusted to COL. To the point that by now most former 'Iron Curtain' EU members have surpassed Portugal in workers income both adjusted and absolute.