This is a BS narrative that needs to die. Yes, relatively early on it was known that that something happened in roughly that area and roughly that time, but that's far from knowing exactly what happened. I fully believe that this information was provided to searchers roughly when it was known. I would expect the families also would have been told at the time.
HOWEVER, until the wreckage was actually sighted or reasonable hope of survival (based on life support) was exhausted, there was no proof they were dead.
Nothing different here than any other SAR operation - if the neighbor's house falls in do you just walk away and say obviously they're dead or do you try your darnedest to find them just in case?
Likewise, completely appropriate to withhold the information while rescue efforts were ongoing, for exactly the reasons seen here - people can't be troubled to understand the difference between indication and proof.
This is also complicated by the systems, sensors and data in question being classified, so details are not available for public discussion.