Java has always preferred introducing features late over introducing something that they later can't get rid off anymore. Whether something is truly useful can often be said only in hinsight. Streams are in the standard library after all.

To enable more rapid iteration, it would have been smarter to place it in a separate package of a `jdk.*` module (like `jdk.httpserver`) for which weaker compatibility guarantees apply. But that would completely divorce it from the other collection classes. Fixing that would require adding extension methods to Java.