It seems as crazy to me as how we can offer in-flight satellite-based wifi but not GPS tracking.
Satellites don't track either ships or aircraft, except for huge nuclear-powered RORSATs that watch the fleets of rival superpowers.
However whilst many trans-oceanic aircraft do have VHF / UHF datalink uplinks through the Inmarsat satellite network the majority use line-of-sight UHF transponders ( beacon-tracking ) to supplement radar ( skin-tracking ):
https://fr24.com/2016-05-19/00:28/12x/MSR804/9c0b766
Transponder interrogation is often referred to as "secondary radar" but that's a misnomer that unfortunately took hold in the industry. It relies on 'squitting' a generated response, not on reflections from the aircraft structure.
So we were tracking the plane but then the plane stopped transmitting tracking info for some reason (no idea if they even had it on primary radar). Someone could have turned it off or the plane could have crashed.
They should position the tracking hardware outside the plane making it relatively tamper-proof mid flight.
Oh wait. Flight number is 804: 8 + 0 + 4 = 12
66 people aboard: 6 + 6 = 12
Must mean something!
str('66') + str('6') = '666'
it's the devil.