I worry about the same thing. I will say, however, that I worry more about this in the context of news articles, conversation, and other shorter-duration activities. Books are a big commitment, and it is highly disappointing to find out someone stretched a 50 page book into 250 pages to get it published. Sometimes it helps to instill the idea, or provides useful elaboration, but sometimes it is filler with no discernible benefit to the reader. Our time is important and as such, I think there ought to be a referendum against wasting it. That is not to say all content should be short, but that it should be no longer than it needs to be, and that information density should be as high as is tolerable.