They either feel like they don't care, or - and, this is likely more the case - they just don't think about. How many times have you left a place and someone says, "Call me when you get home" or to work, or wherever, and you don't call them when you get home or to work or wherever?
I don't think this is just a kids thing or and uncaring kids thing. I think it happens to everyone. It's more of a human thing.
I have to wonder how that might have been different if Gleason had been arrested for aggravated kidnapping.