That’s just wild to think about. We should all strive to build solutions that plague our descendants with their persistent utility.
From a pure safety point of view, it's easier to deal with older, but well-understood products, only updating them if it's an actual safety issue. The alternative is having to deal with many generations of tech, as well as permutations with other components, that could get infinitely complicated. On top of that, it's extremely time consuming and expensive to certify new components.
There's a reason the airlines and manufacturers hem and haw about new models until the economics overwhelmingly make it worthwhile, and even then it can still be a shitshow. The MCAS issue is case in point of how introducing new tech can cause unexpected issues (made worse by Boeing's internal culture).
The 787 dreamliner is also a good example of how hard it is. By all accounts is a success, but it had some serious teething problems and still has some concerns about the long term wear and tear of the composite materials (though a lot of it's problems wasn't necessarily the application of new tech, but Boeing's simultaneous desire to overcomplicate the manufacturing pipeline via outsourcing and spreading out manufacturing).
Why would you assume they're not? I don't know about aircraft specifically, but there's plenty of hardware that uses components older than that. Microchip still makes 8051 clones 45 years after the 8051 was released.