This seems to be one of those "why don't you just be productive?" arguments, which tends to miss the point of why someone did something to begin with. There's a reason Star Trek fans learn Klingon and not a real language, they're fascinated with Klingons but not a real culture, so the energy to learn, say, Basque, was never there to begin with.

I feel similar with history, if I am just doing it for entertainment I'd much rather learn a constructed history rather than the real one.