Performance of npm outdated vs npm update

[falco467]

While trying to optimize our update script to run faster I realized pnpm update will always do a full resolution step, even if the lockfile is up to date and there are no new top-level dependencies.
pnpm outdated on the other hand runs blazingly fast and immediately communicates if any package is outdated. Also npm install will run instantly if node_modules and lockfile are up to date.

Why do we need to do a full resolution step if pnpm outdated can figure out very quickly there are no outdated packages? I am thinking our update script could be a lot faster if I just run pnpm outdated and only run pnpm update if the former produces any output?

Am I missing something important, why npm update cannot use the shortcuts which npm outdated and npm install are using ?