Microsoft didn’t publicly explain the move (we’ve asked for comment). However, ZDNet heard that the company pulled books from its store in a bid to “streamline” its focus, much in the same way that it backed out of digital music. The Microsoft Store is mainly alluring for its apps these days, and dropping books would reflect that priority.
There’s also a technical reality that may have prompted the change. Microsoft has touted the current version of Edge as ideal for reading, but it won’t have as much of an advantage on that front when it switches to Chromium. Simply put, there might not be much incentive to compete when Microsoft is facing off against e-book giants like Amazon and doesn’t have a way to stand out.