Why, specifically? Because they don't know what SarbOx really and truly demands of them. They only know what the consultant said long ago, and they know when the PM says they would be "out of compliance" with SarbOx if they did so-and-so instead of such-and-such.
That's why SarbOx is a boogey man: it's huge, it's legal (rather than technical) and That Enron Dude Went To Jail because of it.
The nature of boogey men is never made clear, now is it? From Lenin to Mao to bin Laden, the DoD has its boogey men used to scare Congress into funding more and better toys. SarbOx is a boogey man in exactly the same way.