is that they never sufficiently explain why some giant empire is expended the resources and effort necessary to kill the entire population of some tiny village.

I'm not sure which is actually worse, no explanation or the ridiculous, 'prophesy made me do it and I am accidentally causing said prophesy to be fulfilled' nonsense.

 

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There are a few books that give pretty decent explanations as to why villages were wiped out. Feist used a good one when he wiped out Talon's village in whatever book that was...book 423 in the series or something. And, Michael Stackpole wiped out several populations wholesale in his series that starts with Dark Glory War with resources or keeping secrets given as reasons.

*edit* In fact, I really can't remember the last time I read a book where no reason was given for that kind of destruction. Hunger games, also used the trope (District 13 was wiped out as an object lesson in response to an uprising..etc.).

I would wager essentially all books give *a* reason but my complaint is I don't think that reason is typically sufficient to justify the expense the evil empire is undertaking. Not to mention rational people don't go off in to the middle of nowhere and destroy pointless villages on a lark.

I think it ties back to the monolithic evil empire trope where they are presented as having unlimited resources and being evil for the sake of itself.

Some author's come up with a decent reason and occasionally it actually ties in to the plot and makes sense but a lot of the time it seems contrived at best. You can tell when the author really doesn't have any clue how to justify but understands its stupid when they make it a matter of prophesy.

 

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That's the lucky thing about evil doers in books, evil characters don't think like we do. I tend to agree with what your saying, but, as always, I'm a bit more lenient than you are. Merely an inadequate reason for the destruction isn't enough to annoy me if it fits the personality/society of the antagonist(s) that are doing the act. If it seems out of character and there isn't a good reason, yeah, then I get annoyed.