Why the assumption that it would be high risk?

Because of the extremely high failure for small business startups. If a business has the capital and the people to get registered with the SEC, then the failure rate is lower. And if some small investor buys SPY, the risk of a total loss is almost non-existent.

And the sad truth is that most investors would be better off buying SPY than investing in anything else. Trump certainly would have been, with the 100 million his father gave him.