Why do I need a node_modules folder?

I came here, because I want to generate a package-lock.json from a yarn.lock, because I want to use NPM instead of YARN. Obviously, I have not installed the dependencies yet and I should install them with a lock file. I tried to use synp, but it's only for someone who has already the deps installed, but why?

Shouldn't everything the package-lock.json needs be in the yarn.lock, already?

No files, tests, or entry points are named in the issue. Start by tracing synp's conversion path and its dependency-resolution requirements, then determine whether conversion can work from yarn.lock alone and define tests for generating package-lock.json without installed dependencies.

Written by the indexing model from the issue text.