The most valuable thing I learned in school, kindergarten through university, was how to learn. If my learning had stopped at the time I finished high school, I would have had only enough to survive; if it had stopped at the time I finished college, I would have had enough to hold down a steady job; but in neither case would I be doing what I do today.
In the same way, a developer that can only reuse code from a Google search can survive, a developer that can program decently in a number of languages can hold down a steady job, but a developer that can differentiate themselves by their ability to deeply understand a business need or language or technology can excel.
Learning for learning's sake is useful onto itself--the brain muscles that are exercised when a person learns the violin are the same that become exhausted learning deep domain knowledge.