At this time of year it is easy to encounter thunderstorms that can only be "flown over" by a U-2 or SR-71. I doubt any current airliner can top a 60,000-ft (12 Km) CB. My wife was SLF on a flight Sat. that was "dodging" thunderstorms, not flying over them. And that was over dry land in daylight, not a big swath of solar-heated ocean in the black.
The ITCZ is the birthplace of Atlantic hurricanes. We Yanks tend to be aware of it, since we are at the receiving end of the output. It's a rough place, and this is the beginning of its most active season. It can form a "wall" of storms that would require a 400 NM (or more) diversion to go around.
I'd put money on a weather-induced in-flight breakup. But the exact sequence of events and contributing causes (WX radar failure? Airframe failure caused directly by extreme turbulence? Airframe failure due to overspeed caused by loss of control?...etc.) may never be clear.
Which doesn't rule out something different - that's just the way I'd bet now.
I'm not sanguine about finding the FDR in a random part of the Atlantic that may span 100 square miles of water 2 Km deep. But maybe someone will get lucky...