well to be fair, the introduction of the old gods, was just that... an introduction, on the last 5 min of the last episode. They only met by discovering the spy of the old gods in the beast country so to speak (there wasnt really a challenge). It would be really easy to spin that and just go on with other races leaving old gods for later. But yea, there isnt much material for ngnl to get a 2nd season yet, unless they go the original story route, which i doubt.
I suppose the same things goes for denmachi, dont think there is enough material to cover another season right now, may be wrong but as ln goes, the first season covered what 4 or 5 books (if not more)? and the manga still has to catch up. Different story is for mahouka, plenty of material for nother season if not 2 more.