IRC still works fine 30 years later, in case you were wondering.
This is probably the key, as they're happy to keep using simple, proven tools that worked for decades and will keep working.
They're not worried about "scaling", "microservices", creating problems so they can solve them and brag about it at conferences & on the (seemingly mandatory now) engineering blog, etc.
It's just a bunch of people running the thing in their spare time and their incentive is to make it so that it requires as little time investment as possible, instead of over-complicating the stack on purpose so they can fill up their resume with buzzwords.