Because most startups fail. Venture capital is a bulk business. Look at how YC works.

As a way to rid yourself of excess funds, it probably works? Likely more effective than a sailing habit, unless you get into racing.

But there's no need for it in your investment portfolio. Pick a mixture between 20/80 and 80/20 stocks/bonds, buy index funds and you're good. Easy and scalable... This works for normal money too, but you probably want a meaningful amount of cash and you may want to more carefully choose your stock/bond ratio. Maybe if you've got tens of billions you might need something else, but it'll probably work for that too.