All I’m saying is that some schools do not see a need to communicate after a decline—even gracious schools. I don’t doubt that you had a bad experience with one school, but that school was “bad” for the reasons you experienced prior to your declining admission. Their “silence” after your decision was independent of your prior experience, most likely just SOP for the school.
Declining NMH felt bad to me, and I wrote a nice note explaining how impressed I was, etc. No response and none required. I still think highly of that school.
As you point out, “of course” the “gracious” school was following up to see if you’d give up where your child chose to go. That is part of their data collection and future yield protection. Done in a gracious way, of course.