MH370 has not been found anywhere near it's last established position because it is not there.
I would not exclude the possibility that the SAR was just unable to find the plane at that location. (currents, debris burrowed in the ocean floor, lack of appropriate resources, bad luck, choose one). I may have missed something, but it seems that there ain't an official source confirming that signals were in fact received after the last known position. Just unnamed "sources".
Regards.