Comment by bbarnett
There is no single "the government".
Instead "The Government" is like a huge community. They are all supposed to adhere to the same code, but like any community there are those members that look for a way to bypass the law, without quite going over it.
That's what said purchases are. And even parts of the community in the same branch of a government department, may do what other parts are not even really aware of. Or agree with.
Although you have a valid point, I object to your calling it a community because communities don't have constitutions and cannot throw people in jail if they break the community's rules. Also, a community has much less control over who becomes a member of the community than a government has over who it employs.