When I think about the pros and cons of a static library folder and a package manager I feel like the library folder is a better approach.

Pros I see with a library folder:

1. No need for an external tool to manage packages.
2. No internet connection required to build.
3. Faster build (no package checking).
4. Simpler environment (less knowledge required).

Pros I see with a package manager:

1. Helps with complex dependency trees (and that can be managed downloading a dependency together with all its dependencies).
2. Helps checking if there is a new version available.

It seems the industry has decided to follow the package manager path for almost everything built today. So, what am I missing?