Accuracy is almost never the right statistic. Here, profitability is. As soon as you realise the target statistic applies a human-goal-value-weighting to the prediction outcomes, it should be easier to see why ML systems are often unsuited to the task they're set. Here, those 5% of cases are likely business-ending or business-making: precisely because they arent naively routine.
Also worth noting that the arithmetic expectation is only a good way to measure the profitability if we are talking about small amounts compared to your total wealth. For any other case, you should use the geometric expectation of total wealth to evaluate options. (This is equivalent to maximising log wealth, the Kelly criterion.)