The first reason why rules are different is because in one case (IT) you're dealing with a seller-customer relationship, and in the second (Finance) you're dealing with a investor-company relationship.
Second, public equity markets are a heavily regulated environment, for many reasons, and require strict rules to function to avoid widespread fraud, market manipulation, insider trading, etc.
This is similar to Healthcare as well. You can't just go selling a random untested drug claiming that it cures cancer.
And they should be different because of different configurations of power and impact. Investing isn't just buying a product or a service, it is allowing someone to use your money freely within certain conditions.