The glory of being a criminal justice lawyer is being a hero of the moment. One of the most stressful things that can happen to a person is to get served...and also to be served with a certified letter of process to notify that someone just filed a lawsuit against you. It might as well read, "Heeeeere's Johneeeee!" in blood and play the Freddy theme. That letter signifies an assured drain on a person's financial resources and emotions, not to mention newfound circumspection. It doesn't take long for neurosis to set in when you ask people how they're doing, and you keep getting the response, "That information’s privileged," or that you need an attorney present while you text (autocorrect for defendants). Pretty soon you'll catch a glance from a random group of whispering and laughing high school students and be left wondering if your fly was open.
Now imagine that same experience reflected in the criminal system's eye. This time, you get served...and processed into jail. There's no time to reflect on how to approach the situation, talk to family or friends. The criminal justice machine just knows one thing: by the book. Exceptions to the book only mean trouble for the Government down the road, so it is in its best interest to stick by the safe path, the beaten path (which, unfortunately, sometimes means the beat-you-up path).
You're one individual, subdued by the potency and resources of the State. You could be innocent; you could be guilty; but those issues aren't for the police to decide. All police need is "probable cause"—that is, a "fair probability"—that you violated any law, and you can be arrested. Even if it turns out that probable cause is lacking, that question won't be reached for several days. In the meantime, you'll have very little freedom of motion in jail, and practically no expectation of privacy, even in your conversations, which likely will be monitored. So "who you gonna call?" Enter the criminal justice lawyers. These are the people who will protect your liberty when its back is to the wall.