Oh sure, the format is standardized. The semantics aren't however, in any practical sense. What happens when you vendor/patch/fork a dependency? What happens to vulnerabilities that are not in code paths not used by your software, or only under certain flags?

HTML is standardized too, how many documents do you think use the p or i tags properly? Heck, how many documents do you think are HTML5 compliant, even ignoring the semantics?

(And even if it were, it is still much too bulky of a tool to replace lockfiles. Having to add a kilobyte to your file every time a bunch of new vulnerabilities get reported in your deps recursively sounds like a great addition to your commit history.)