I work at a telco. We have many museum-grade Unices in production, mostly AIX and Solaris - we even have a Wang still running in one of our datacenters. It's largely a case of there isn't a business case to migrate it to modern hardware - one day we'll no longer operate a legacy copper PSTN network, but until that day comes, we still need it all. We still have maintenance contracts on some hardware, like our Sun Fires. It's very clear that replacement parts are scavenged from whatever they can find second hand.

I recently rewrote the system we use to push user accounts and passwords to systems that don't support LDAP. It was amusing to write an app using a current-day stack on RHEL 8 that purely exists to handle these very legacy systems.

One of my favourite systems I've had to work on is running Solaris 2.5.1. Users are added to the program by editing the source code and recompiling it. How times have changed.