Perhaps they want to keep their options open. For example, they...

Perhaps they want to keep their options open. For example, they can install a large battery (Northam is specifically described as "battery-ready"), charge it from the solar farm, and sell (dispatchable) power from the battery on-market when prices are highest during the evening peak or when there is a shortage in supply due to say a coal-fired generator going off-line.

One of the main advantages of a PPA may simply be to lower the perceived risk as far as lenders are concerned. If CCE already has the finance secured, then the need for a PPA is not so urgent.