The design of Java is focused on code maintenance. That's exactly what young developers lack experience in. They know how to write greenfield code, by themselves. They haven't yet looked back at code they wrote and said, "ugh, what the hell was I thinking?"

Since Java was developed the world has shifted to accommodate a lot more rapid development and code you throw away rather than maintain. But experienced developers also know how often "prototypes" are still around decades later.

Java is also not perfect, and a lot of new languages are conscious of its faults. But the reason it's still around is that it's core principles are oriented to code that sticks around.