Why disable window exit button?

I have noticed that some software disables the window exit button. On MacOS the window exit button is the Red X in the upper left side.

This forces me to browse thru the application for another way to dispose of the window.

An example of this behavior is the iPhone simulator. The iPhone simulator is a tool used by developers to test their software without having to own all different physical devices. It does not have ads or other reasons Apple would want to make it difficult for me to exit.

Why do the designers disable this button on some applications?