Upgrading a code base because of language evolution is pure cost for most people. It's a relatively risky and almost zero-reward exercise for mature applications.

You've got 3rd party library/dependency drag, tooling drag (everything from IDEs to CI/CD pipelines), development effort for code changes or QA and testing resources. Your engineers have to invest time in learning about the language and library changes. Never mind that unless you do a total rewrite, you end up with an incoherent code base which mixes old and new styles.

All this busy work/effort could instead be applied to adding features, eliminating bugs, improving performance, etc. - changes that end-users actually appreciate or that add business value.

Java conquered the enterprise precisely because it was slow moving and stable and offered unparalleled backward compatibility. Pretty much, the very same reasons Microsoft windows conquered the business world. This is (was) Java's strength not the weakness you portray.

Let's face it, at this stage Java is never going to be "cool" again the way it was in the 90s. Trying to join the "move fast and break things" school of language evolution just makes it look like a middle aged person (I'm one btw) trying to be "hip" by emulating young teenagers in dress and speech. At the same time you're alienating your existing users.