But how would that work?

Say I have software written that runs just fine, but has not been updated to the latest runtime of Python or Node (as per your example). Perhaps a dependency I use has a broken recent version, but the old version I use works fine. You remove the package, now it breaks my software. This would effectively make it so that all libraries / dependencies that are "abandoned" by the author or inactive, would be deleted, which then results in all the software that used them to also break.

Unless I misunderstood something?