It might be that any potential hijackers were hoping the story would die and it just be written off as a loss over water.
The world is a big place, and not all of it covered by radar. There are lots of islands out there.
If I were a terrorist who wanted a plane as a weapon, I would hijack a plane in an out of the way part of the world, try to fake a crash, and replace passengers with extra fuel for the 777 to extend its range. On last nights episode of VICE, we see huge amounts of fuel that was supposed to go into power plants just standing there.
I would put as much fuel on board, and try to disguise the plane as a standard airliner under a different name. Keep that second set of passengers (if any) down, and fly to New York as normal--then divert at the last moment--no hijacking mid-flight in that would be a giveaway.
Early nukes were complicated affairs. A big airliner could hold a primitive gun-style device no problem
As pointed out above you need roughly a kilometer of runway at minimum to land a 777 on (high altitude, wet, heavier load of passengers and fuel) and more run way is going to be needed.
That runway is going to also need to support the weight of an aircraft that with passengers, luggage, cargo and fuel is in the vicinity of 200 tonnes.
Not something you're going to find on a small island.