In addition to campaign contributions to elected officials and candidates, companies, labor unions, and other organizations spend billions of dollars each year to lobby Congress and federal agencies. Some special interests retain lobbying firms, many of them located along Washington's legendary K Street; others have lobbyists working in-house.
A quick perusal of who lobbies most will give you some idea why certain special-interests like the Medical, Banking, Defense and Media establishments have their way with our government, and through it, the rest of us.