Those systems sort-of, kind-of worked, and got plenty of press, but vanished from the market without much of an obituary, or post-mortem exam, AFAIK.
My guess is that they were impossible to maintain.
I'm waiting to hear that the problem is now licked for the current crop.
Rather more than that. For a famous example, check out the wikipedia article on MYCIN (a classic of the era):
MYCIN was never actually used in practice but research indicated that it proposed an acceptable therapy in about 69% of cases, which was better than the performance of infectious disease experts who were judged using the same criteria.
https://en.wikipedia.org/wiki/Mycin
There were many practical reasons why expert systems fell out of grace (although like others say they are still used widely, in real-world applications) but a large part of them was political, rather than anything to do with their effectiveness.
Some historical background:
https://www.researchgate.net/publication/3454567_Avoiding_An...
In the end, the problem with expert systems was probably that they didn't scale as well as one would hope -primarily because it's damn hard to develop and maintain huge hand-crafted databases of knowledge solicited by experts who have very little incentive to collaborate in the creation of a system that will put them out of work.