Sorry Python but it is what it is.
How is it not a lock file?
package.json doesn’t contain the exact version number of all downstream dependencies, this does
Lockfile contains exact state of the npm-managed code, making it reproducible exactly the same every time.
For example without lockfile in your package.json you can have version 5.2.x. In your working directory, you use 5.2.1, however on repo, 5.2.2 has appeared, matching your criteria. Now let’s say a new bug appeared in 5.2.2.
Now you have mismatched vendor code, that can make your code behave differently on your machine, and your coworker’s machine, making you hunt for bug that wasn’t even on your side.
Lockfile prevents that by saving an actual state of vendor code.