You are totally wrong. When they come after people a lot of times there case is not as air tight as most people think. They accept pleas all the time with the writing saying the defendant saying it is not a plea of guilt and the government specifying that there is no admission of guilt. The defendant will agree to a payment but it ends up being way less than a drawn out trial would cost.
Tons of people who truly believe they are innocent take these pleas to save time, money, stress and worry. Even if innocent, instead of fighting for hundreds of thousands of dollars and risking a jury conviction, it’s easier to agree to pay a lesser amount and keep your record clean. The feds agree to this when their case is not very good.