Why in the Eurocentric white nationalist movements is there such a large emphasis on the Nordic mythologies over the Greek/Roman?
because we are mostly Anglo-Saxons, Dutch, Germans, Irish and Scots. Our traditions derive from the Germanic tribes and the Celtic tribes. that is our heritage and our way, unavoidable even if we choose to be christian. We have named the very days after our Gods; Tuesday, Day of Teihwaz. Wednesday, Day of Woden. Thursday, Day of Thunraz. it would be larping to pretend we are latins or achaens. their cultures are great ones, and we owe them much, but that does not mean we need to become like them and abandon our own native gods. that is not how paganism works anon, it is a national religion.
and I have to admit the Greek/Roman is so much better than the Nordic, in terms of storytelling and aesthetics
they are very much the same to each other because they have common roots. but what the greeks and romans have in terms of sheer material and poetic composition, they lack in terms of a strong core morality, which germanic culture provides, and which even tacitus admitted was a strength of the germans
For where so many laws have failed to maintain virtue in Rome, German morality has prevailed at making Germania a chaste land
as an example of what I mean; when the Aesir (and their Aryan devotees) first came from the East and conquered the Vanir and their Neolithic cults, they incorporated the Vanic gods into the Aeseric pantheon, but they forbid the previously acceptable customs of incest, homosexuality and polygamy (Heimskringla, Ynglingatal). there is nothing quite like this in greek mythology, where sexual deviancy is explitly spoken against. only vague ideas in tradition, like that Venus curses the unchaste and the homosexual with STD's (hence the term Venereal disease) but these were only ever folk beliefs, and never fully a part of the grec-roman religions, which sometimes even glorify homosexual, pederast or incestuous relationships