Yes, it's in many ways exactly that popularity that's the problem. The ratio of good to mediocre programmers hasn't really changed any, but now there's a whole lot more JS devs out there, so finding the good ones is an exercise in wading through a sea of mediocrity. For better of worse, the Java developer ecosystem does a better job of filtering out the mediocre devs, and generally once you reach a certain level of experience picking up something like JS becomes a trivial exercise. We tend to favor candidates that have experience in multiple languages because it's a strong signal that they're a quality developer, and you tend to find more of that in your backend developer pool, where the frontend developer pool tends to have a lot of experience with a ton of frameworks, but they're all almost exclusively pure javascript focused.