Because the US does it on a bigger scale than anyone else.
The US government is bigger than most other governments (and bigger than the population of some nations).
More stuff happening + more people involved = more opportunity for **** to go wrong.
Name another case where you've heard of someone charging a one million percent mark up on a government contract?
You mean governments getting ripped off for millions of dollars by unscrupulous individuals?
Or just plain spending of the peoples money on hookers and blow?
Both Happen fairly often. You can probably google up a half dozen scandals with ease.
A while ago here one senator decided to give 2 million dollars to a local airline for it to resume flights to the territory... which it did for a month, with empty flights that didn't so much as carry government traffic.
We got nothing, they got our cash. Don't hold your breath waiting for any criminal trial.