Migration tools aren't panacea they don't fix stackoverflow answers, pdfs, blog posts, existing tutorials, talks, slides, examples, mailing list posts, or irc logs.

They also require locking a codebase and making massive changes all at once.

It should be preferred to just add them as -Xlint:XXX warning / -Xlanguage:XXX features that can be opted into, along with a tool that will automatically update the code to best practices.

This way no legacy codebase has to undergo the massive cross-cutting refactor required when running a migration tool, instead they can opt into the features they want, and new users copy pasting in code will see that code work.