Courage and honesty
Governments of all political colours have been proven down the years to be awful at making investment decisions. So why do they still do it? I think the answer is that they are scared of being asked the question "what are you doing about X?" and being unwilling to give the courageous and honest answer, which is: "X is not a matter in which government should be directly involved. It is for the market to decide".
Instead, the knee-jerk response from politicians to every question has to be: "look how much money we are spending on X. Aren't we great! Vote for us!"