For people who work with legacy technologies, it can actually be the reverse situation. Yeah, your knowledge of The Latest Hipster Web Framework becomes less valuable year on year, but the situation is a little different for senior personnel running Fortune 50-level ops on legacy technologies. They aren't exactly churning OpenVMS systems architects out of coding boot camps. It's a lot the same situation as COBOL programmers are in - they're not something you need a million of, the work may not be 100% stable, but when you do need them they're fixing mission-critical systems that have millions/billions of dollars of business riding on them and the rates are astronomical.