Being able to get books easily and change the font size, and font if the font is bothering me, makes it more enjoyable for me. Being able to carry a huge selection of books with me so I have choices if a book starts to bore me makes reading more enjoyable for me. Also, my e-readers are lighter than most books I read (I intend that word to be in the past tense), and easier to hold, plus I don't have to hold the pages back with my hand. I have some carpal tunnel syndrome in one hand and I do find that a bit easier. They're little things but I do enjoy reading more with a lightweight e-ink e-reader than with a book. I did not enjoy reading on my iPad more than reading a book. It was too heavy and the wrong size for me, plus the backlit screen is harder on my eyes.
It isn't a big deal, but it's enough that I'm reading much more than I was.