The typical reason for poor procurement outcomes is the who-watches-the-watchers-ad-infinitum problem.

At stake: huge amounts of money

Naturally, people will go to great lengths to try and obtain that, by influencing the key decision makers.

So you put in a layer above the decision makers.

So they influence the layer above the decision makers.

Repeat-repeat.

The only true defense against corruption, at scale, is competition. Because then everyone tries to knife each other in the back, and it generally zero-sums.