There is a buy america act, which requires the government in buying from American companies, there are also federal similar laws which might be the reason here
Nobody gets rich when government workers do something, it’s outsourcing which enables significant wealth transfer from government to private individuals. That creates huge incentives and means it’s those same companies try very hard to influence the rules.
A fraction of those government workers are people for whom the politicians intervened to alter the hiring process in their favor. You're heads in the sand if you think the politicians aren't getting favors in return either up front or later.
The difference between in-house and contracting out is only the difference between lump sum and a monthly check.
By comparison thousands of people at federal contacting companies are making over 1 Million per year. Further those companies pull in billions in profits.