Damage caused by a bomb, missile, un-contained engine failure or mid air collision does not necessarily mean a catastrophic in flight disintegration, with a significant amount of wreckage that would float.
So those who theorise since no wreckage has been found at sea level around the point of loss of contact that none of the above could have happened, should be more equivocal.
Nor do we know that any of the above events could have been reliably picked up by a surveillance satellite tuned to monitor "flashes", especially a brief flash from a small bomb that could be shadowed by the body of the fuselage.
The US say they have monitored some faint electrical/RF activity on the plane which they say was connected with engines running.
We do not know why contact with this signal was lost, the plane may either have crashed, landed and shut down or travelled out of reception range and so it could have continued on its way for a further hour or more.
They say they couldn't derive the heading of the plane from this signal so it may have turned again.