While the service POMs are being formulated the information is kept "secret" in order to free the programmers and decision makers from outside interference/influence, that includes outside influence from senior leaders within the service. The data is not necessarily "secret" in the traditional sense: Such material would cause "grave damage" to national security if publicly available. Some people during the programming phase of the budget formulation (where programs can be cut or decremented to use as offsets) have no qualms about tattling to the Hill. Which brings undesirable attention to the PPBE process.

The NDAs are no doubt being put in place so people keep their mouths shut outside of class. It doesn't stifle debate nor restrict the chief's role to provide military advice. It's to prevent the debate from showing up in the Post or some Congressman's daily brief sheet. This type of “gag order” can actually assist in the debate since folks can readily talk with the assurance they will not be quoted outside the forum. It's also the reason the DAWG is always conducted on a non-attributable basis.