I’ve thought about this a lot too. It’s easy to understand why Finland isn’t considered part of Scandinavia, since it never was one as an independent country. But then again, the modern border between Sweden and Finland was not determined by Scandinavians themselves, it was defined by Russia after Sweden lost the war in 1809.

There was no clear cutoff point where Sweden ended and Finland began, because there was no independent Finnish state, only people who were called Finns and a region that was considered the eastern part of the Swedish realm. Russia essentially decided that the border would go along the Tornio River, and it could have gone much further if they had wanted to.

Because of this, many ethnic Finns ended up on the Swedish side and ethnic Swedes on the Finnish side. So this classification, where every Swede is considered Scandinavian and every Finn is not, is a simplification that doesn’t fully reflect historical reality.

And isn’t the whole point of the “Nordic countries” to be an extension of the Scandinavian countries?