The point is that the command-line is the most direct, succinct way to make the computer do something. Most GUI programs are not good when it comes to repeating a task hundreds of times on different data. At best, they will do it slowly. At worst, they will have an awful interface that requires twenty minutes of clicking, if you know what you're doing. Often times they can handle the single iteration but not the loop. The GUI's author expects the user to handle the loop. The mouse is highly inaccurate, the keyboard is accurate. Pressing the enter key is much different from moving the mouse pointer over a region on the screen and clicking the button. We don't measure people in terms of CPM (Clicks Per Minute); we use WPM.
There _is_ software to do it for me and it's called an interactive shell. I can manipulate thousands of images with one typed command line. Or I can manipulate thousands of _insert_data_type_here_ with one typed command line. Being generic is great; no need for multiple, disparate, complicated GUIs. No fuss.
In many ways GUIs are more complex.