Both lotteries and casino gambling are heavily regulated in terms of their returns to consumers, and there are reasonable methods of recovering value if they fail to perform as promised, because the entities are generally still operating.
You can't do that with business investments -- there's no way to mandate a particular minimum return to investors, and no way to recover lost funds if the business fails to perform as promised. If I promise you safe 15% returns, and then I run the business in a high risk way and it goes under, there isn't any way for the state to really regulate that level of risk and return except in very highly regulated industries like insurance where money is being invested in rated securities (and even then, it's not great.)
The biggest problem with private investments is that there generally isn't any liquid market to provide a "real" price. It's just whatever the company can convince an investor to pay. Nobody can short or sell you their shares easily, and if you buy in it can be impossible to sell out.
You can't do that with business investments -- there's no way to mandate a particular minimum return to investors, and no way to recover lost funds if the business fails to perform as promised. If I promise you safe 15% returns, and then I run the business in a high risk way and it goes under, there isn't any way for the state to really regulate that level of risk and return except in very highly regulated industries like insurance where money is being invested in rated securities (and even then, it's not great.)
The biggest problem with private investments is that there generally isn't any liquid market to provide a "real" price. It's just whatever the company can convince an investor to pay. Nobody can short or sell you their shares easily, and if you buy in it can be impossible to sell out.