One of the things with a NCNS is that if you don't call in before two hours prior to your shift, you still get marked as a NCNS. Say that you have to be in at 8am.....you have to call at six. There are days when you don't feel well and decide that you'll wait until the alarm rings to decide if you'll go in.....but you usually don't set the clock for two hours before you go in.
Or, if you are on your way to work and there's a car accident, or you have car issues, then it is too late to call in....and even if you do (to say that you are on your way) you still will be marked as coming in late. So, sometimes I can easily see why people don't call in.
Often, at my store someone will call off but the LOD may forget to tell anyone else that a TM called off. Sometimes we don't know that someone called off until they don't show up for their shift.....and then we ask if anyone knows about "TM X" and the LOD says, "Oh, I forgot to tell you that X called off.