Yes, digital files can be backed up, copied and distributed at will; but the problem with digital permanence is it really takes a surprising amount of work. Work which most people are unaware they need to do, or which falls by the wayside because it really can be time consuming and expensive to do properly (guilty on that count, here). Multi-million dollar businesses with dedicated IT departments even fail at this sometimes.
Most people stick their photos on their hard drive or Facebook and call it done. The more diligent might copy stuff to a CD/DVD or keep a single backup on an external drive and think they're safe. Very, very few will have a coherent backup and ongoing data migration strategy such as nonuniform described above (costing $1000 every year to maintain, not to mention the ongoing effort to keep things current!?! Ouch.)
I've been around computers since 1984. I've had data stored on audio tape, weird 3" disks, 3.5" floppies in a myriad of formats, CD and DVD, SmartMedia, CompactFlash, SD, MicroSD and an assortment of hard drives in different formats. Files which were never copied from tape are gone, the tapes long since deteriorated (though oddly enough I do still have that computer and it still works). The 3" disks, which I found in a box recently? No hardware to read them. The 3.5" disks? My ancient PC was one of the last to have a disk drive as standard and even then only the ones in MSDOS format are potentially readable. CD and DVD? The better quality ones from up to 15 years ago are still OK, but some have failed, in some cases very prematurely and I have no guarantee that others will not follow. Hard drives - which interface? Which format? If I found a SCSI drive in a shoebox today, I'd not be able to plug it into any computer I own without a great deal of extra expense and effort. Even then it might not be readable, or intact, or contain anything worth saving. If I find a PATA drive in a box a decade from now, what are the chances it'll fare any better than the SCSI one does now? The PATA drive installed in my old (and apparently, dead) Commodore A4000 isn't formatted in a way my PC can deal with even though it will plug in. What about the current SATA standard, eventually it too will be supplanted and disappear, as will its replacement and whatever follows that. Is it really going to be worth my grandchildrens' time and expense to access the data stored on some old dusty antique hard disk or near-forgotten type of memory card on the off chance that it's still readable and had any real value to begin with? Somehow, I doubt it.
But they'll be able to pull my photo prints and negatives and contact sheets out of the next box and see what they were without additional effort (they might still chuck them away, but at least they could make an informed decision in doing so!)
Yes, the pace of change is slower than it was when I started in computing, but things still change and "old" hardware, media and data formats fade into unsupported obscurity. Data will be lost if it isn't actively taken care of. I'm under no illusion whatsoever that future access to a TIFF, JPEG or especially RAW file's content is a certainty even if it does reside on media that is readable. Perhaps it will be, perhaps it won't. History would suggest it won't. By comparison, my negatives and silver gelatin prints ought to outlast me and will remain "readable" without obscure hardware or software.
As for keeping things safe from disaster, I could always file the negatives somewhere safer (safety deposit box?) and put up with the loss of some convenience in access.