There's also nothing stopping teams from developing the front-end in Java too. Java SPAs have been possible for over five years using TeaVM:
It lets you code in Java, compile to a native SPA, and gain all the benefits you'd expect from a single, strongly-typed language top to bottom (refactoring, POJO reuse on the front end, etc.).
There is a full intro article in Java Magazine:
https://blogs.oracle.com/javamagazine/post/java-in-the-brows...