Easy to learn language and don't have to worry that much about memory, seen as a modern replacement of C in userspace, coroutines are easy to use and suit the lifecycle of network applications.
Java ecosystem is rather large, there have existed AOT compilers since around 2000, even if they had a price tag, and naturaly modern devs are allergic to pay for tools.
Those devs are now served with GraalVM and OpenJ9, as free beer AOT compilers for Java.