Several reasons. 1. If you live in a terminal it's easier to stay in that terminal instead of switching to a new window to deal with your task manager, then switching back to your terminal. 2. It's quicker to type one command with all it's options instead of using a GUI and selecting multiple options. 3. IN my case as a blind programmer I find it easier to use as many command-line tools as possible instead of dealing with possible accessibility issues in a GUI.