Yes I know. It is really annoying to have treants and blood worms snatch my atonement crits. Its not really a big problem or anything but so totally unnecessary it irks me every time I see it happen.
But back to topic: When you are shadow there is no reason not to use massdispel as you can use the glyph without giving up anything of consequence. As Disc you have alternatives for the glyph and some other classes sometimes like to dispel (had shamans tell me not to do it because they wanted to before) or can do it with less impact (shadow).