The major problem is that when you learn something in this current crazy JS/Front world, your knowledge is deprecated 6 months later. I know a developer should always stay up to date with technology by constantly learning, but if I compare what I learned 5 years ago in Python, I would say 95% is still relevant today. But if I look at the JS "state-of-the-art" stack today, compared to the 2 years old, it's completely different. It's very frustrating to invest time and effort to learn something and then hear recruiters tell you things like: "Hmmm no one uses that anymore".