Shut it down!!! They’re doing that anyway!

True, but the issues you’re seeing are mostly in trade publishing, where the books aren’t really meant to last forever anymore. You may notice that a high end coffee table book however might be sewn not glued, and the binding will lay flatter. The glue is sometimes what’s causing the problem.

This is also a paperback reduction and the text has been shrunk to fit a smaller trim size. It doesn’t always work well.

Some designers center text on the page with equal margins on either side. It looks ok while designing but when the book is bound, part of the margin gets glued in. I learned to make interior margins slightly larger than the outside. Some people weren’t taught how to do that.