Especially because the 'strong warrior culture' in fiction is often based on RL historical propaganda, not reality. The Celts, the Germans, the Mongols, they all had fairly robust civilian economy and infrastructure - your average Northman probably spent more time tending his farm than going Viking abroad.
Ehhh... yesn't.
It is of course true that no civilization or culture ever has subsided solely on war. Indeed, the base for all peoples and cultures is how they get food and other necessary things. Therefore, of course most Norse were farmers and most Mongols were herders.
However, that is not an either/or thing. The Romans, too, would know that the German
ics were farming back home... and then during the campaigning season in summer they would go and raid their neighbours. Which, of course, early Rome did likewise with
its neighbours in Italy. That is the crux here - that all the farmers in those cultures are
also warriors, with little division of labour: Near-everyone is a farmer, there are only small populations of craftsmen, merchants and other specialists, and the farmers are also all warriors.
Of course the economic
backbone of nomadic steppe peoples were their herds (replace "farmer" above with "herder" for those cases). But raiding their settled neighbours, or getting a 'Danegeld' or, ehem, "diplomatic gifts" from them, pretty much was also an integral part of their economy. That wasn't just an extra that happened now and then, that was pretty much part of the expected and required income. And likewise, in Norway, during the "Viking Age", everyone went viking (which was a proession, a raider/merchant, not an ethnicity) so much that it caused economic problems back home due to labour shortages. There were even law codes established that
curtailed going on overseas adventures... and that all shows of course how large the amount of the population was that took part in those expeditions.
Saying that most of them were farmers or herders is hence not a counter-argument. The terrifying thing is indeed that near the entire population would be potential warriors on raids or in battles, just with a "civilian job" for the off-season.
Of course, that doesn't really translate well to sci-fi, where such a structure would lead to absolutely superfluous amounts of military manpower while disturbing the all-important war industry back home. These days, wars are won on equipment, logistics, the war industry rather than people, manpower and morale, after all (well, compared to historical times, that is - those things are still
important, of course).