[alerighi]

Freeing memory (or running a garbage collector) has a cost associated with it, and if you are freeing memory (or closing files, sockets, etc) before exiting a program it's time wasted, since the OS will free all the resources associated with the program anyway.

And a lot of languages, and for sure newer version of the JVM, do exactly that, they don't free memory, and doesn't run the garbage collector since the available memory gets too low. And that is fine for most applications.