The problem is when someone writes one viral blog post, then decides to pad it out and sell it as a book. If you can find the original post, you get the entire substance for free in ten minutes.
It's funny when popular blog writers get criticised for turning blog posts into books (usually while leaving the original posts accessible) when I feel this is way more honest than doing exactly what you say. Resilient Management by Lara Hogan and An Elegant Puzzle by Will Larson do the former and are two of the most useful SW Management books I've ever read.
If there is enough content to fill a book, then it's fine. The issue is that usually, there's enough for about two chapters, and then it's just padding.