The disk is likely more cost-effective ( if only they'd continue to manufacture them ). Flash memory also degrades a lot faster than disk, especially if not read periodically.

A well manufactured laser disc can easily last 44 years as -somewhat- proven by the history of the compact disc. A solid state memory chip that can hold over 10 gigabytes of data -at a reasonable cost- cannot say the same. Maybe really good quality chips that nobody would ever pay for alongside a game could last 20 years, but realistically 10 years is a stretch without rewriting the data.

Even Switch 1 catridges are a bit suspect despite most of them being less than 32GB in capacity & thanks to scale being much much cheaper than anything GoG will be able to get their hands on for this.

I mean yes they could get manufacturing costs down to $3 per unit I'm sure, but that kind of defeats the purpose of anyone ever wanting to have a physical copy of a game. I think discs are just a much better long term storage medium.

Flash memory data retention isn't that long unless it's periodically powered up, the higher the levels per cell the worse it is (so, SLC - single level cell, where each cell only encodes 1 bit with 2 values - has far longer memory retention than QLC - quad level cell, where each cell encodes 4 bits with 16 values).

Meanwhile as somebody else already pointed out, stamped CDs and DVDs will last decades (this is not so for recordable ones, though if I remember it correctly even those last longer without content corruption than QLC flash).

As I see it, GOG would have to themselves provide the service that makes short custom runs of physical game DVDs complete with cover art and then ship it.

Economies of scale make a single company doing all the work of physical production cheaper and more effective than a ton of companies (including some - indies - generally too small to have the scale to do it) doing it independently, and whilst subcontracting that work should be possible, it would still be more costly than just one company doing it for everybody plus there's still the shipping part on top of the manufacturing part.

Of course, this assumes that things like DVD masters can be made cheaply for short runs (yeah, using recordable DVDs is possible but those are much more costly than stamped DVDs plus their last a lot less).

Without all this, I don't really see how, for example indies would be able to participate in this even if they wanted to.