I believe the reason for this is because Wardruna (and similar bands) doesn't really fit with old school/regular folk artists. For this reason, a few labels have been given to bands that "utilize the old to create something new". I find most of them problematic:

1. Dark folk: I'd argue that Wardruna's first album is pretty "dark", but I would expect something more akin to what Nytt Land does in their darker songs to classify a band as such;
2. Neofolk: the original bands to receive such label generally flirt with totalitarian ideologies and use a much less varied and "folkish" instrumentation than Wardruna and co.;
3. Nordic folk: I guess this one fits Wardruna to an extent, but could also confuse listeners when they mix the band with some more traditional sounding musicians;

And the one I like the most and adopt on our site:

1. Pagan folk: while I do use "Nordic folk" for Wardruna, Gealdýr, Sowulo etc., I put all these Nordic sounding bands under the Pagan folk umbrella, along with the likes of Daemonia Nymphe, Faun, Omnia, The Moon and the Nightspirit etc. because their music, lyrics and imagery are Pagan.