It is typical vs organized crime, because you don't want to let them know that you are collecting state witnesses. But four years is too long. It started when Trump won and the DoJ feared that he will fill the vacant positions with his judges. All bad actors, like the admins for Hillary's server, were granted immunity as state witnesses. There were some slap-and-seal cases (slap on the wrist for a scape goat, case sealed forever), the rest is pending as sealed indictments with gag orders.