Nobody can be put on trial for a very serious crime, unless a group of people called a grand jury first decide that there is enough evidence to make a trial necessary.
When the Seventh Amendment was written in the 1700s, $20 was considered a lot of money. Today, any disputes that involve amounts less than $75000 will not be handled in a federal court.
The national government does not control these areas because they are not mentioned in the Constitution, and so they are under the control of the states.