You can read here why the peer deps were introduced: https://nodejs.org/es/blog/npm/peer-dependencies/

Imagine this structure of packages:

  your-app/
  ├── dep-a/
  │   └── dep-c
  ├── dep-b  
  └── peer-dep

Very simplified: `dep-c` is dependency of `dep-a`, so it is installed in its node_modules, but `peer-dep` is peer dependency of `dep-a`, so it is in node_modules of `your-app`. `dep-b` could also define `peer-dep` as its peer dependency, so it is installed only once. When npm switched to flat node_modules structure, peer deps become somewhat redundant, but not quite. Pnpm, which uses symlinks to achieve proper node_modules structure while avoiding long filenames, combined with auto install of peer deps would be ideal package manager.