That's anecdotal evidence. What you are reporting is the exception, not the rule.
Virtually all recorded CDs, DVDs, magnetic tapes, and cassettes will be gone after 40+ years since their average lifespan is just a fraction of that. Even the ROM modules inside older cartridges will have a hard time lasting that long because even though they are hardware encoded and can't be electronically changed, the transistors themselves can and will eventually fail, no matter how much care you put into it.
Most PS1 disks are rotting already. In 15 - 20 years, a lot of Switch cartridges will no longer be functional. And so on.
A bit much my dude. CDs and DVDs can go up to about a 100 years. As well as tapes, which are known to have exceptionally long lifespans... but it all depends on use, wear and such. So it is up to an individual to how long something can last. And if you ask me, 100 years is a long time and i'll be dead before any of my games are I reckon.
Also, transistors and such can always be replaced. They can still make the electronic parts you need to fix your cartridges (and put the rom back on the cart pretty much). Cartridges from decades ago still work as well, but again, it depends on use. Lastly, the 15 to 20 year number for Switch cartridges is based on nothing.