The blog post is rather oversimplified and abrupt.

It's not just about shelf space. While not perfectly linear, the associated costs grow significantly with a book's length. It's about how long it takes to print a book and how much materials are needed per book. This part can be quite insignificant compared to the rest.

Then we get to the logistics. It's a question of how many books can fit inside a single box, how many boxes can fit inside a single truck, and how many boxes or truckloads of a specific book are even required. Then we get to the store where the question is about warehousing and shelf space that the blog posts talks about.

Now, there is also the point about audience (and publisher) expectations in terms of how long a book should be and how much they should cost. If the book is too short for its genre, it may fail the audience expectations. Then again, a longer book should cost more, but audience and publishers are less willing to take a chance on unknown authors. When an author has name recognition, they can sell more books and the economies of scale kick in.

Then you have the issue of authors becoming less concerned about writing perfectly paced stories without any unnecessary scenes, with their editors becoming less scrupulous about minor details, etc. that all lead to books bloating (especially with later installments in book series).