Outside of web applets, set-top boxes, and DVD players, JVM didn't really do much sandboxing. On the desktop or server, it did practically none.

I think the rest of your sentence was "by default" which is the same thing the comment you're replying to said: "security gets in the way of everything"

One could always launch any java process with java -Djava.security.manager -Djava.security.policy=someURL and it would sandbox a huge number of things (see: https://docs.oracle.com/en/java/javase/17/security/permissio... )

The problem is that defining a reasonable policy for any modern app is a gargantuan pain -- as is the case with any security policy language -- so as the GP said people hated it and now it's dead https://openjdk.org/jeps/411

I think a key part of solving that is by not thinking of it as a set of security enforcement rules on top of the preexisting platform, but as a new platform (that just runs everywhere). So, instead of ACL listing what files can be accessed, shove it in a sandbox where the app has its own files, and the platform open file dialog enables the user to authorize one-time access to individual files.

You basically can't take a complex thing and write complex security rules for it and expect success & real world adoption.