NPM creates a node_modules folder and then fills it with the libraries that your app has specified. Then each of those libraries has their own node_modules folder and NPM will install the dependencies of that library and this happens recursively which is absolutely crazy. The directory structure is A-5.0/B2.0, C-3.0/B2.0, D-3.0/B2.0 which leads to B2.0 being duplicated three times even if it has the same version. Almost every package manager uses a completely different strategy. First of all every package gets a globally unique identifier (in NPM package identifiers are relative to the node_modules folder of which there are many). Usually it is the name of the package and if a package manager needs to support multiple versions of a library within the same program it just adds the version itself to the identifier. This means that if you need B2.0 then it would be stored in node_modules/B/2.0/ and libraries A, C and D would use that single version.

The NPM community is well known for their one liner packages with most of the work done in the dependencies. If that one liner has 5 dependencies and your project transitively depends on it 5 times through react or something then you end up creating 5 times as many files than are needed. It's very easy for a trivial application that uses NPM to have a million files in the node_modules folder.