For example, many nuclear power plant in the west were built 40 years ago. Amongst the myriad of sensors, devices in a power plant, I think that most of them are outputting ASCII logs. There are still readable today. (Same can be said about avionics, space probes, etc.)
Now imagine yourself 40 years from now on, trying to fix or reverse engineer a very legacy system, you will have to recompile a journalctl from 40 years ago before being able to read anything.