I'm not sure if this is only an about accessibility to non-tech people.
Think about it: You can't get files on your device in a useable format anymore. This means piracy becomes exponentially harder to consume (i.e. you can't use your iPad [easily] as a reader for your pirated ebooks). Quite honestly, that's a stroke of genius and likely a secondary motivation for this workflow.
You can very easily use your iPad as a reader for arbitrarily downloaded ebooks. Go to Gutenberg or Archive.org or the pirate site of your choice. Select a book. Select the format. Epubs and PDFs have the option of being sent to iBooks. Mobi can be opened with a compatible reader app if you have one installed. And the file can be saved to Dropbox or whatever file service you have installed. With the latest version of iOS (IpadOS) you can save to your Downloads folder or even to a connected storage device, or to a file share on your local network. You can also load books via Dropbox, local network, or connected storage.
I do this all the time. For me, it's convenient to use Dropbox as the intermediary, but there's plenty of other ways too.
What? You can very easily use your iPad as a reader for pirated ebooks. Like, I cannot understand how it could possibly be made smoother than it is.
Whether pdf or epub, and whichever device or type of device you use to add the file, once you do it will automatically be stored in your icloud and synced across devices. Same as any purchase.
This is not true any more. I can go to a music blog on my iPhone, download a zip of an album to my phone using the Safari download manager, unzip it in place with the core iOS file manager, move the resulting folder into the media library folder for my music player app, and play it on my device.
I can later open up the iOS file manager and find the mp3 for my new favourite song in my music player's folder, click Share and send the file to my friend on Telegram or whatever.
Think about it: You can't get files on your device in a useable format anymore. This means piracy becomes exponentially harder to consume (i.e. you can't use your iPad [easily] as a reader for your pirated ebooks). Quite honestly, that's a stroke of genius and likely a secondary motivation for this workflow.