Most plausible reason. National security hawks have always been extremely protective of intelligence even when the risk is tiny. Probably some DoD people (or person) wanted to keep it closed and new hawkish leadership let them do it.

Who knows, the Navy hasn't released any statement beyond "cyber security risks" so there's only politics to fill in the blanks.

It seems to be this agency https://en.wikipedia.org/wiki/Fleet_Numerical_Meteorology_an...

Who recently got a supercomputer system https://www.montereycountynow.com/news/local_news/a-new-supe...