I use prime because I have enough need for the shipping aspects of it that it works out favorably. Prime video is a very nice bonus.
Beyond that, there is a lot of hassle to being connected to Amazon. All their e-readers and audible can't help but advertise incessantly. These are apps where I want to open to the same place maybe a hundred times in a row as I read or listen to a long book. Yet, every time, it opens to the store page and I have drill down through my library to find my current book. If I'm on to my next book and search for it while in the library section of the app, it will pull up results from the store as well.
Ads are a pain on Kindle though I could admittedly spend the money to make them at least partly go away. Music I don't really care about as I get Apple on another bundle.