Earlier quoted context omitted.
The point is that the paperback can sit on a shelf for 100 years be readable. An ebook takes a migration plan to remain readable. Yes you can remove DRM, but libraries cannot, they have to keep paying, and they're being sued to prevent them from preserving and migrating their data.
More than just DRM, random bit flips are a problem too. One that's been thought about by places like the Shoah Foundation.
You're backup's only good if you can successfully restore it.