If you like to do business economically you can study economics, but there are many successful entrepreneurs who do not go to universities that they are rich from their own experience as well as their bravery so the need to study economics is not necessary.
Also because they didn't waste their time on study on how they can earn money. They only have hardwork and of course strategy in life on how they can get a profit. Specially they've focus only on what their goal from non stopping until they achieve what they aiming for.