Yeah, and there are a lot of people who are most likely guilty who never even get charged. A prosecutor won't want to take up a case when he thinks the evidence is in the zone between "preponderance" and "beyond reasonable doubt".
If the prosecutor can get somebody to plead guilty before they are charged, then he doesn't even need to think about the value of the evidence--or, indeed, about whether the person actually did anything. A guilty plea is even better for his reputation than a conviction, because he can get lots of those done in a day.
Sure, somebody who looks prepared to lawyer up often won't be charged.
