[systemtrigger]

Speed and reliability. Take open source. You could manually find, download, untar, configure, make, install and track dependencies. A good package manager lets you do that in one command e.g.:

  $ brew install package_name

OSX includes a package manager for proprietary packages blessed by Apple. It's fast and reliable but its curators forbid most open source and proprietary packages. It's called App Store.

[evilduck]

Ignoring the problem of software availability, the App Store also lacks a fast command line interface. I can kick off a homebrew package install process and return to whatever I was doing faster than the App Store.app launches.