Reminder: Most devs actually care about the things they make. This is a management/timeline problem, not a developer one.

Probably performance - the Java server takes up a lot of memory and CPU for what it does. The base implementation first started in 2011, so it wasn’t exactly designed to be multithreaded or parallelized because most games were still largely single-threaded at the time. Rewriting it from scratch in a different language probably helps with that