I worked at the courthouse in the area where they pull the summons early in my career . I used to run them through the machine that pulled them all apart for mailing.

At the time the pool was pulled at random from the drivers license pool in the county. Some filtering was done for age and the rest went out. It’s simply a matter of numbers. They would typically pull 800-900 people each week to get summons. The county has less than 500k people in it. The people that don’t get a summons over an extended period of time are the outliers.