"Black Boxes" are designed to float, and usually have some kind of beacon attached to make recovery much easier.
Though what things are designed to do, and what they actually do can be different things.
Otherwise - I'd say the problem is that it was an airbus.....
I don't trust those planes.
Of course - by that same token, I don't trust a lot of the commercial aircraft - particularly the older, fatigued airframes. You've got a lot of
former military people working on those birds, and they are used to the 100% materials inspection that goes along with milspec products. The civilian
end of the bargain isn't 100% screened, and with the horror-stories to be told about military aviation... it doesn't make me incredibly confident
with the commercial industry.
As for the cause - it could be anything - a mechanical fault/failure; a flight control system error (certain flight parameters can cause the system to
get confused and think it is stalling when it isn't - and those programming oversights like to rear their heads at inopportune moments); or a fault
in the grounding systems that are supposed to harden the plane against various electrostatic and electromagnetic problems.
Or the Chinese just tested a new ASAT weapon in a place no one would suspect.....
Or the Greys were repossessing some of the technology we loaned from them......
Pick your insanity.