I guess Kindle policies are getting more restrictive...I switched to a Kobo ereader 2 years ago and love it. Buh-bye Amazon. I just read some of this thread below with someone complaining about the Kobo UX they tried in...2013. Kobo integrates with Overdrive (libraries) & Pocket & Dropbox & Google Drive. Drop a PDF or epub etc into a cloud folder and it shows up on your Kobo.
Can your Kindle do that? (I don't know but I doubt it.)