I know that's not what you wrote... because you said that the system was rigged. However, there is another (more likely) explanation - that the Federal prosecut

I know that's not what you wrote... because you said that the system was rigged. However, there is another (more likely) explanation - that the Federal prosecutors only bring cases to trial that they are likely to win. Out of the pool of possible cases that they could bring to trial, they only bring a fraction of those to trial. But the ones that they do bring are the ones that they feel they are more likely to win. The reason that they can win or settle so many of their cases isn't their extra resources (which can be vast). It's that they are selective in the cases they choose. This ends up being self-reinforcing too - the more cases that they settle, the more the reputation that they have a strong case, which increases the likelihood that the next case will settle. Their extra resources come into play when evaluating a single case, but when looking at the population of possible cases, it is their selectivity that skews the percentages in their favor.