One can point to a fundamental error by the crew in not noticing the rock - it was on the charts albeit well disguised - however looking at the whole picture I think it was an entirely predictable error. When there is only one slice of cheese between safety and an accident, the hole will be found fairly often even though (or especially when) it is caused by crew error. Adequate flight safety is only ensured when there are several slices of cheese whose holes don't normally line up - and even then it can happen. This operation had too low a safety margin / too few levels of safety for routine stuff, and we have unfortunately seen the consequences. I wonder who provided operational oversight? It was definitely an accident waiting to happen.