I have almost a thousand epubs mirrored on my NAS (and backed up elsewhere). The device I read them on changes periodically, but the actual ebooks don’t wear out, are easy to transport, and get much more use than my physical library. I still love paper books and would never part with mine, but they are more like mementos or even artwork to me now.
My paper books are heavy, get dusty, almost died in a flood once, can tear or be stained, are a fire risk, and would be very difficult to replace if anything happened to them.
Digital preservation has its challenges, too, but acting as steward for epubs has been much easier than for paper books (for me, anyway).