The rationale is chillingly simple, if it costs X to put things right and Y to pay for things going wrong and X>Y, then the lowest priced option (in this case Y) wins and it is considered a cost effective way of doing business, moreover if, in the process, the blame can be laid at someone else's door, then so much the better.
They (the Treasury mandarins) know the cost of everything and the value of nothing.
Agreed. However, there is such a thing as a "duty of care" that stretches far beyond the estimates of the bean-counters. It is incumbent on those who wear uniform and have rank to do the best for their subordinates, whether career-limiting or not. The chilling rationale of the Treasury has been blown apart by the Collins ruling which now gives personnel some protection in theatre, although this is subject to appeal by disgracefully mendacious ministers. The Collins ruling makes it more imperative that those in positions of responsibilty speak out and, if rebuffed, keep a paper trail handy.