What exactly in the process doesn't make sense?

Unless the comment has been edited, it does make sense (other than the fact it's intention might just be an ad for BookShelves reader):

- Use Calibre to cross-convert books.

- Leverage public domain ebook catalogs: Standard Ebooks, Internet Archive, Gutenberg.

- For on-device reading BookShelves app might be an option, with no cloud lock-in.