That's because the title was editorialized.

The original title "The Thinner Book: Atomic Habits by James Clear" is explicit on its nature:

> The most important ideas in your typical 300-page book can usually be distilled into several pages. These several pages are the thinner book.

There is a role for summaries with different levels of detail. The short capsule summaries are useful(for one thing, it is easier to remember) and your link itself is a great example.

But, there is also a role for longer summaries, which are still short relative to the book, but include useful points and some of the illustrative examples not present in the shorter summaries. Reading a 250 page book has ample scope for the mind to wander and lose track of the important issues which is not an issue with a 10 page summary.

Further, summaries at this level are less available, and it would be a good thing if more books had such summaries. (The downside being people might be more likely to skip the original book and the author is not rewarded - this can be corrected to an extent if the author themselves give these shorter summaries at the end of the book or as a separate short book. Also, some others might be motivated to get the original book after reading the summary).

Here's an automatic summarization in 20 sentences.

https://smmry.com/https://www.chrisbehan.ca/posts/atomic-hab...

7500 might barely be considered a novelette. But if you're going to categorize non-fiction in fiction terms, the most comfortable length category is short story, which usually goes up to 10k.