The answer is simple, according a report from The New York Times.
Groninger is one of the few companies that sells filling machines that can fill in a wide variety of materials, including concrete, wood, paper, glass, metal, and even plastic.
It has more than 40,000 customers, according the Times.
The Federal Trade Commission, which regulates the industry, says Groningers are more efficient than private companies.
The Times reports that GE, which is the manufacturer of the federal filling machine used by the government, uses GE-branded machines.
The FDA, which certifies products, says that the GE machines are superior.
The report also noted that the federal government pays Gronings for the labor it employs, and it uses GE machines to fill its orders.
This arrangement helps the government to pay for supplies, as well as avoid the cost of providing machines to other suppliers, the Times reported.
However, it also raises questions about whether federal workers should have to pay GE to fill their orders.
According to the Times, some federal workers and contractors have filed class-action lawsuits against GE, claiming they were cheated out of their wages.