Because you either aren't selecting the active window as the area to capture or you aren't using the crop feature to only have the relevant information in the screenshot.
As I said you need to practice off-line and get familiar with the program before using it live for images attached in the forums. The scribble tool you used is inadequate as the email is still visible, you need to adjust the width of that tool so it is completely obscured. I would suggest that until you familiarise yourself with this program, that you modify your post and remove the image attachment so your email address isn't hanging in the wind.
I don't know if that screenshot application allows you to select an area and 'blur' or 'pixelate' the area thereby obscuring your email address or even selecting the area of the email address and selecting/deleting it from the image. There have to be lots of ways to do this, but you have to familiarise yourself with this program.
I don't use that screen capture tool, so I can't offer any practical assistance and in reality that has to be down to you to learn how to use the tool than have others try and teach you how to use it.