Interesting. I have the opposite experience. I had two schedule changes on KE award tickets and got calls from Delta both times.
I find calls annoying especially when I travel in a different time zone, roaming etc. I mentioned it to the first agent that I prefer email instead of call, but she had no idea how to set it up. For the second change I hanged up twice, because I was on expensive roaming and busy. A few minutes after my second hang up I received email with updated ticket and itinerary.