The reasons are that your book will instantly be available on Amazon and their royalties are higher than other distributors — especially if you use their «purchase» button
on an external website like your blog.
Not exact matches
You may wish to direct students to leave feedback for you
on an
external site, much
like TripAdvisor, rather than have a reviews section
on your own
website anyway.
In the World Wide Web it's always a copyright infringement but
on mobile, applications
like Pinterest or Facebook leave you navigate through
external websites without leave the application itself, so I'm not sure.
Users, of course, will still be able to put in - game items up for sale
on the Steam marketplace, but it looks
like the time of offering up digital items
on external websites hoping to score big is now over.