The picture of the MFD NAV screen does seem to point at why they didn't notice the rock - it's all very well to say they should have noticed the absence of returns beyond the rock but you are asking them to notice something is missing from a display which is far easier said than done.
The 3rd generation helicopter seems to have a problem of too much information and perhaps the SOP should be to have the simple radar picture on the MFD without the FMS overlay.