I thought this too, but then I started to give it a try to read on a kindle paperwhite and just put it on flight mode while reading a downloaded book.
Some advantages in my opinion:
- Most of the prices of e-books are just cheaper compared to the prices of physical books
- The kindle paperwhite is just smaller than physical books, so I can just put it in a pocket. It just saves space also. Just imagine 1000 or more of physical books in a bookshelf in a room which just takes space
- I can read and swipe through the pages while I’m standing somewhere with one hand (e. g. commuting in a public tram)
- If I want to start reading a new book right now, I just buy it, download it and start reading it in few minutes compared to waiting until the delivery of the physical book (this is the biggest advantage for me)