Where I’ve seen these systems most in my work is connected to scientific instruments, where the manufacturer would rather you spend another half million dollars for a marginally improved model with more recent io and os support vs shipping a patch for the machine you already paid a quarter million for 15 years ago.

The system being slow and old doesn’t matter. It is running xp and airgapped. Sometimes you access the data by usb stick or burning a cd rom. The software stack it runs mainly dumps sensor data onto a flat file so its not really necessary to be very robust. And sure the ancient optiplex desktop idling all day drinks more electricity than a modern light weight chip, but that couple dollars more a week if that in electricity costs is hardly a concern in research setting.