You aren't getting it.
This isn’t Apple’s fault and Apple has nothing to do with this issue and is NOT responsible for anything that a third party app developer does or doesn’t do with their app.
Your issue is with Amazon. NOT Apple.
This is Amazon, alone, that has made this decision.
The message you get is just a generic Apple iOS App Store message that applies to any other apps with a similar situation.
This is NOT an Apple problem, but an Amazon one.
Apple has NO control, whatsoever, over what ANY third party app developers do.
Your “beef” is with Amazon, NOT Apple.
That stated,
I am not sure what your issue is, as I still have my older Kindle app on my iPad 2 and all of my purchased content.
Did you remove the Kindle app from your iPad 2 for some reason?
Assuming Amazon has left older versions of its Kindle app on Apple’ s iOS App Store servers, have you tried restoring your older Kindle app by going into the iOS App Store App and under Purchases, look for Kindle app in that list of apps and then tap the download “cloud” icon next to the app icon to see if you can re-download the older version of the app this way?
If you had the older version of the Kindle app before, already, then using this method should restore the app to your iPad 2, but only if the older version still resides hidden on Apple’s iOS App Store servers.
Best of Luck to You!