Betting and knowing under conditions of uncertainty

Why is high probability knowledge a more accurate tool in decision-making than high-probability gambling?
In other words, why does it make sense for a judge to convict another person based on witnesses who were in the area (whose chances are small that they were mistaken for a person or just this one) but not based on a bet. For example, there is a group of prisoners who beat up a guard while one prisoner tried to stop them. Each individual prisoner has a high chance that he beat up the guard. Let’s assume that the chance of each individual prisoner being part of those who beat up the guard is equal to the chance that the witnesses in the first example I gave were mistaken. Why does the fact that in the second case the decision was made through a bet and in the first case the decision was made under the knowledge of a high probability make any difference?