It seems to me that there's an obvious reason the fuselage broke -- the airplane crashed. Presumably in breaking, the fuselage absorbed some energy that otherwise would have gone somewhere else. It's conceivable that it will turn out the fuselage wasn't overstressed and shouldn't have broken, but it seems much more productive to assume it was overstressed, and ask what that tells us about the crash.
Of course, if the fuselage broke before the crash, it would be an entirely different story. But no one's suggesting that, presumably for good reason.