It is the responsibility of the developer who added the dependency, or the person who reviewed the PR that added the dependency.
If neither of those are around it is the responsibility of the person who took over either of those responsibilities or the person who now maintains that package.
If that person isn't around then it is unmaintained, and should not be used.
If that sounds complicated it is because it is. In any given package you might have 1-100ish people with responsibilities, but they also have sub-responsibles that they might not know about.
The package management system has no responsibility except to serve the exact version of the exact package you requested. If you expect anything more from them you are not looking for "package management" and npm is probably not the right place to look.
This is one of the reasons I try to not have transitive dependencies in JS projects.