"The subtle art..." is one of the first books I think of re: filler, too, but I do think the filler can have value as a way to spend more time with a valuable idea. Many of these books contain some valuable idea that could have been completely explained in a couple of paragraphs, but then you wouldn't have a built-in way to spend a couple of hours with the topic to give it time to get a little deeper into your psyche.

In a way it's equivalent to packaging a small item in a larger box to make it easier to keep track of. Wasteful on the surface, but there's an undeniable value to it that would be hard to achieve more efficiently.