With aircraft navigating by signals from satellites and sending out ACARS messages [sorry if that's the wrong terminology], almost in real time although at a cost if I read correctly, does the technology not exist such that it should be mandatory (as with carrying an ELT) that an a/c broadcasts at least its lat/long, alt, speed and heading every 10 seconds (or other short period)? That would seem to me to give the powers that be immediate notice that something had gone badly wrong and greatly narrow down the area of search for survivors or wreckage
It is all about cost. Bean counters do a cost/benefit analysis, and come to the conclusion that crashes are so rare, the cost doesn't justify putting the equipment in the aircraft and paying for the satellite communications that would be needed. Sad, but very true.