More specifically, I would like to know why this eBook is not compatible with the Kindle Paperwhite.
It says that it is a print-replica with the additional features given by X-ray which is compatible with the paperwhite.
Why is it not compatible?
The book in question is a "Print Replica" textbook. See how it says
Networks: An Introduction [Print Replica] [Kindle Edition]?
When we look up information about Print Replica:
Kindle Print Replica textbooks maintain the rich formatting and layout of their print editions while also offering many of the advantages of standard Kindle books.
Each page in a Print Replica textbook displays words and images in the same position as the corresponding print edition, while adding Kindle features such as annotations and the ability to sync your last page read across multiple Fire and Kindle devices and Kindle reading apps. Kindle Print Replica textbooks also have most of the same features as PDF-formatted books, including advanced zoom and pan functions.
Kindle Print Replica textbooks are supported on:
Kindle Fire Kindle Fire HD Kindle Fire HDX Fire HD Fire HDX Kindle for PC Kindle for Mac Kindle for iPad Kindle for iPhone Kindle for iPod touch Kindle for Android Tablet Kindle for Android Phone Kindle for Samsung Tablet
Kindle Print Replica textbooks will have the words "Print Replica" next to the book title in the Kindle Store.
Also, with regard to the "Look Inside" preview having adjustable text sizing, note the little FYI at the top of the previewer:
Just so you know... This view is of the Kindle edition (2010) from Oxford University Press, USA. The Kindle Edition edition (2010) from OUP Oxford that you originally viewed is the one you'll receive if you click "Buy With 1-Click" on the left.
So it looks like the preview is not of the same exact Kindle file that you'd be buying.
I also downloaded the sample of that book onto my K4iOS app, and it's totally fixed layout, with margins containing notes and illustrations and stuff, while keeping the text fully searchable. This kind of thing generally isn't supported on an e-ink reader.
In general, ebooks that aren't available on the Paperwhite and other eInk readers are not available because those titles contain content that cannot display on those devices. This frequently means that the content is a fixed layout, rather than a reflowable, file. In the case of the book that you linked, that does not appear to be the case based on the Look Inside functionality (since you can increase the font size there). This may not be meaningful—Look Inside is not a 100% faithful representation of the ebook.
Other types of content that would not be usable on the Paperwhite et al include: audio, video, and any interactivity (such as problem sets that readers can answer in the ebook or graphs that change based on user input).