It would take an even more bizarre set of circumstances than hijacking to explain the behavior of the plane as we know it so far.
Transponders: disabled to deal with fire or as a result.
Closest possible airport: the one the plane turned towards was arguably the best one to go for.
Radio silence: disabled by fire.
Fr. Occam is pacing back and forth and stroking his beard on this one, that's for sure.
Or they could apparently have taken a second to activate the 777's Emergency Locator Transponder, powered by its own battery and with its own hardwired, non-computerised switch circuit to the cockpit.
You could imagine the aircraft accidentally flying (and transmitting over SATCOM) for hours with no other communications if there was some kind of crisis that completely cut off the pilots' (and passengers') ability to use the flight controls for the whole time (quite possibly by killing them) without damaging plane's systems much overall. Hypoxia or smoke inhalation seem plausible. Some kind of fire that completely destroyed the instrument panel without spreading too much further sounds vaguely possible. (IIRC at least one of the pilots had a habit of smoking while flying.) Surely both pilots couldn't somehow have locked themselves out of the cockpit behind the security door? The problem is that such a scenario is hard to square with a flight path that apparently included multiple changes of course and altitude long after any initial cockpit emergency https://news.ycombinator.com/item?id=7420894 .
That does raise the question of how many turns there really were, though. Earlier reports based on radar suggest that the plane made several course changes as it flew in a zig-zag around the Malacca Strait and Andaman Sea west of Malaysia. If enough of those apparent sightings can be knocked down then an accident becomes more likely. Though even one change of direction onto one of the final SATCOM arcs, apparently without any effort to communicate at the same time, is a real head-scratcher if you assume no foul play at any stage.