BECAUSE THEY WANT TO BE CONSIDERATE TO THE HARD OF HEARING?

I don't know. My mom used to do her replies to my e-mails in all caps so that she could tell which bits were her and which were me, until I explained the yelling convention to her. For awhile it was a little upsetting to keep getting e-mails that said things like, "HAVE YOU CALLED YOUR GRANDPARENTS?" Fine, I'll call, just stop yelling!