The financial system is currently using the Value at Risk model.
One of the fundamental assumptions of it is that the trades used are normally distributed. The benefit of assuming normal distribution is that it is well known and easy to calculate. You can’t assume normal distribution. Is the height of a large enough population normally distributed? If you believe so where are the 6m tall humans or those less than 0m tall? These are reasonably expected to exist in a large enough normally distributed population.