[Falkon1313]

Even in those jobs, there are always tangential tasks, one-offs, and side projects that could potentially be done much more easily/efficiently using different tools than the primary codebase. Even when using the same tools, different ways of thinking (patterns, paradigms) can make a huge difference.

The tools used to build GUI CRUD apps may be very well suited to that, but sooner or later all that data collected by the CRUD GUI will need to be processed, analyzed, and/or migrated. Although that might be doable with your CRUD GUI building knowledge, other tools or approaches, more well-suited to data processing, could make that task far easier, better, faster, and more reliable.

A legacy system from pre-networked days may be optimized well within the environment that it was created for, but when the day comes to make it connectable with an API, different skills may be useful. If you refuse to learn them, then either you have to hire someone else or you are likely to end up with a mess.