That's the main reason but not the only one, federalism is the other (unless you consider that also a consequence of certain 20th century events, which in part it absolutely is and in others it absolutely isn't). The ID is clearly federal, but almost everything you might want to implement on top of it is not. The Nordics are small enough to country-wide standards easy.
>The Nordics are small enough to country-wide standards easy.
Size of a country has nothing to do with this. Neighbouring Austria is tiny and is also federalized, with each state having several degrees of autonomy and potentially causing various bureocratic nightmares depending on what you want to do.
True, but I'd expect that those smaller units still have it much easier to pragmatically standardize procedure even when those are formally below federal than in larger units.
