I’m a Kobo wanker and it’s easy enough for me - I use the built-in web browser, go to the site, find a book, and download. I think it’s fairly easy to to something similar on Kindles, otherwise there’s some way to download to your computer and send it across.
True, but any that I’ve downloaded from elsewhere - Project Gutenberg etc - tend to be really badly produced ebooks where the text is off, there’s spacing issues, it doesn’t flow properly etc etc. Standard Ebooks take the original text and do a lot of formatting so that it’s actually nice to read.