Several plants have functions still in operation that were part of the original design from the 1970s, or even older. Such solutions are typically based on relays and solid-state electronics that were naturally a large part of engineering education for the current (aging) engineering and maintenance staff.
Knowledge of the analogue systems is important both for the maintenance of existing equipment and for modernization projects, where full understanding of existing/old functions is necessary in order to avoid introduction of faults or unwanted functionality in the modernized functions.
Over time there’s an obvious risk that maintaining competence on the old analogue systems will become increasingly difficult since modern engineering education focuses on other areas.