It was designed this way on purpose. Most criminal justice systems are designed to protect the state. Ours was designed to protect the individual.

In a notable trial in 1728, a defence lawyer (Robert Dundas) persuaded a jury to reassert its ancient right of acquitting, of finding a defendant "not guilty". The case involved Carnegie of Finhaven who had accidentally killed the Earl of Strathmore. The law (as it stood) required the jury merely to look at the facts and pass a verdict of "proven" or "not proven" depending on whether they believed the facts proved the defendant had killed the Earl. As the defendant had undoubtedly killed the Earl, if the jury brought in a "proven" they would in effect cause this innocent man to hang. To avert this injustice, the jury decided to assert what it believed to be their "ancient right" to judge the whole case and not just the facts, and brought in the verdict of "not guilty".

The (re)introduction of the "not guilty" verdict was part of a wider movement during the 16th and 17th century which saw a gradual increase in the power of juries, such as the trial of William Penn in 1670, in which an English jury first gained the right to pass a verdict contrary to the law (known as jury nullification), and the trial of John Peter Zenger in New York in 1735 in which jury nullification is credited with establishing freedom of the press as firm right in what would become the United States.

Although jurors continued to use both "not guilty and "not proven", jurors tended to favour the "not guilty" verdict over the "not proven" and the interpretation changed.

The state has practically unlimited resources to find evidence, interview potential witnesses, and explore legal theories. One of the more important reasons that we require a jury of the defendants peers to find him or her guilty beyond a reasonable doubt is to somewhat offset this enormous imbalance of power.