"I do not understand the caginess, this long after the events."
The "caginess" you cite is a genuine problem. The history of these events -- and many others on the East Coast, involving German attacks during World War II -- has been systematically downplayed by academic historians and by journalists who follow their lead.
I am at a loss to understand why.
The “caginess” you refer to is almost certainly lack of knowledge. The attacks were, in general, insignificant. For example, 9000 balloon bombs were launched from Japan, but the result was 6 deaths. All of the other balloon bombs that reached the US were an annoyance only.