Between the start of construction (2010) and opening of the plant (2014) solar PV dropped in price more than 60% whereas I do not thing the price of mirrors has changed much.

Seems like this is just a case of bad timing - the peak year for installing concentrated solar was 2013-2014 and it has been slowing down year on year since then. Solar PV is still on an upswing in terms of new yearly installed capacity.