Chuck a ebook on any storage medium and wait 20 years, and odds are the file is unusable, due to the file being incompatible with new software, the storage medium being unusable, bitrot or a number of other factors. Maintenance is required for both physical and digital. Physical requires a relatively dry space and not bending the spine, which anyone's grandma's dog can do. Digital requires backups + regular recovery testing to be guaranteed.

There's plenty to worry about with maintenance of both formats, but for paper most of the investment is upfront. For digital it is an ongoing investment, with the benefit of a pristine copy being maintained.