They have a limited lifetime. It's a fairly long limited lifetime, sure, but unless you're reading and rewriting the data on the cards regularly, you can't rely on them to all still be intact a decade down the line.

Which is a shame, because I kinda love the idea of my music collection being stored in a little cube that unfolds to reveal a hundred or so micro SD cards.

Maybe not SD cards but something similar - Nintendo Switch cartridges are a few GB and seem quite durable.

Huh, those are neat! The largest ones seem to use Macronix HybridFlash technology, and:

"HybridFlash provides a very stable medium to contents and OS, enabling storage as long as 20 years at 85 degrees centigrade and it also works normally from 40 degrees below zero to 85 degrees centigrade."

So, not forever, but definitely longer than regular flash memory. Cool.

I'm surprised nobody has made SD cards with mask-programmed ROM or even traditional write-once PROM.

It's called a Nintendo DS game card. I don't know if the Switch game cards are flash or mask-ROM.

I don't have a source, but I think I remember reading somewhere that Switch games are some kind of archival flash, designed for 50+ year retention.

Mask ROM.

Agreed! For anyone else who, like me, didnt really pay attention to SD cards for a few years, it’s quite amazing how cheap they are for their capacity now. 256GB from reputable people like sandisk for low tens of dollars. Used one as a good travel backup drive on a recent work trip.