I confess I don't come from an aviation background but I thought FDR's were pretty indestructible..? Do those in the know agree that an FDR would be destroyed in this manner? Or is it just a matter of "convenience" that the FDR's aren't available to be examined...?
It's unusual but neither unheard of nor impossible for a crash to destroy the FDR. Most unfortunate..
I would point out one obvious thing which you seemed to have overlooked. Outside of a plane crash of this magnitude, can you think of anything in Nigeria capable of generating enough heat to melt an FDR. I can't.