I’ve heard nothing about Flight 93 Memorial plan being rejected or withdrawn, so I’ve got to assume it was entirely intentional.
But something just occurred to me. There were two groups of people on Flight 93. Us and them. Maybe the architect and project managers weren’t clear on who, exactly, was to be memorialized?

Assuredly they are memorializing the Cult of Diana.
I thought that was a symbol of Dread Cthulhu, me.