Good question!
Somewhere in the reports it is written that this was an older FDR, one that used tape for recording, when the tape was destroyed or made unreadable or whatever. Given that we have seen far worse crashes in terms of post-crash damage that FDRs have survived, it is a very, very good question why this FDR should be unreadable, but.... The people who can answer that question are the very ones we mistrust. 'The FDR is unreadable?'
'Oh! Yes, Sah!'
'Umm.... Okay, then!' What else can one ask?
I was just reminded the other day of the fire in the Nitel Building in Lagos. As it happened, I was in the area a few hours earlier to get a photo for a new passport. On the way back to Ikeja I heard the sirens and saw the smoke, so that I must have just missed being in the middle of all Hell breaking loose.
That was a case of financial records being stored in a skyscraper, highly combustible financial records. Big wahallah, nothing finally concluded, back to 'business as usual...' An air crash is very small potatoes compared to that, plus it's plausible that the FDR really is unreadable. This one might be a case of 'Move along! There is nothing to be seen!' Bet on Dana folding to reappear under another name, leaving the families of the victims left stood around looking stupid.