You're kind of right, but there is a different between the default repositories used by apt (Debian & Ubuntu) and pacman (Arch) and things like npm, in that the

You're kind of right, but there is a different between the default repositories used by apt (Debian & Ubuntu) and pacman (Arch) and things like npm, in that they are indeed reviewed and can't disappear overnight. You have some guarantee that it won't disappear overnight, because of the organizations behind them. With npm, anyone can publish/unpublish without any sort of review, while packages in the default repositories are reviewed by others.