@Heinz Gormittz Made a real life stock market where there are thousands and thousands of real stock and filters that you can invest in through him. it is really in depth and more people should check it out.
Also if you were to put a stock market in game let's say you wanted to short sell mushrooms. All you and your gang would have to do is sell all your mushrooms driving the market price down. And you make infinite money just by short selling and driving the market down. To much control over the markets.
But check out Heinzs' real stock market it's great!