Because so many unsophisticated people would "invest" in ponzi schemes, pyramid marketing schemes, and outright frauds. Why shouldn't we let people send their bank account numbers to Nigerian Princes who just need someplace to park their millions? It's their bank account! If they want to risk it that's their business.
Being a qualified investor is good evidence that you do due diligence and fully investigate any investment opportunity. Being "poor" is good evidence you have no idea how to do that. Because being rich or poor probably indicates if you have been ripped off in the past, and will be in the future. When a company files with the SEC or with their state for an LLC, that's pretty good evidence that it's not fraudulent.
BTW: LLCs have been around for 41 years. They sound exactly like what you want, but I guess it's more in the spirit of the internet to rant about the difficulty of something than to actually do it.