How much has been spent on this so far to replace a system that works?
But it doesn't work that well, does it? There have been enormous difficulties over the years caused by (and I generalize) poor availability of the existing fleet (Tutor, Tucano and Hawk have all been grounded for significant periods at some point). I'm not expecting the new aircraft to be perfect but the issues on the legacy fleet have been one of the causes of the carnage in the training system for quite some period.
The other main cause (ie inconsistency at Government level about how many people need to be trained) will create as much havoc in the brave new world of MFTS as it always has done. Something of a shame that the civil serpents couldn't see that when they recommended we take this path.