Amazon told users on Monday that it is killing the "app" it developed for Windows 8 and Windows RT, and was recommending that users upgrade to the older Windows for PC app or switch to Kindle Cloud Reader.
You can find the announcement at the end of this post, or you can find more info on the related help page on Amazon.com.
As for why the app is being EOLed, well that requires some background.
When Microsoft launched Windows 8, many companies rushed out new apps which supported both new versions of Windows, Win8 and Windows RT, or "Really Terrible".
Amazon is one of the companies which took the cheap and lazy approach to supporting Windows RT; they wrapped up their browser-based reading app, Kindle Cloud Reader, and called it Kindle for Windows.
That app didn't work well when it launched, never received the same support as other Kindle apps, and it didn't support nearly as many features as the Kindle apps for Android, iOS, or macOS.
In fact, the Windows 8 app was largely sidelined in favor of the older Kindle for PC app, which ran on everything from Windows XP to Windows 10.
K4PC is that app which got all the updated, including support for Kindle textbooks,etc, while the Kindle for Windows app never even gained support for reading your own ebooks (just ebooks bought in the Kindle Store).
And now Amazon is killing the app which it never put any effort into.
What took them so long.
O O O
For the past few years Amazon has supported two separate Kindle apps for Windows PCs. In order to provide our Windows customers with the best Kindle reading experience, we are simplifying our approach and focusing our efforts on the Kindle for PC app.
If you are currently using our other Windows app (Kindle for Windows 8) on one or more of your PCs, we recommend that you upgrade to the Kindle for PC app to get the best reading experience and latest Kindle features. We are regularly updating the Kindle for PC app, including recent features like multi-color highlighting, improved search performance, and support for textbooks.
To simplify the experience for Windows customers, we will remove the Kindle for Windows 8 app from the Windows Store on October 27, 2016. If you already have the app installed on your PC and wish to keep using it, you can continue to download and read books as you do today. If you uninstall the Kindle for Windows 8 app, you won't be able to reinstall it from the Windows Store.
If you have questions (or if you have a Windows RT device), please see our Kindle for PC help page.