Is it based on political structure, racism, or just boredom like nazi punk? Nazi punk bands
seem very committed. Problem was, like all punk music, they were very boring.
Only about 2-5% of metal bands are worth listening to. No rock music is, no techno is, very little industrial is, and no newer country is.
What does this tell you? Moronic forms of music produce moronic results. Pick something better, like classical, and learn your culture instead of preaching others to keep it up - that's what I'd tell the Nazi bands.
Some Nazis make brilliant music. Darkthrone, Burzum, Graveland, Thor's Hammer, Unleashed, Morbid Angel, Motorhead, Immortal, Emperor, Infester, Therion and others have all expressed nationalist, national socialist, traditionalist, fascist or occult volkisch sentiments. They are different than the imitators who make boring, pointless, angry music.
Interestingly, the failure rate for NS-BM is probably less than that of black metal as a whole, but I still wouldn't run out and get any of it. Legion of Doom was pretty good too.