Traditional investing doesn’t make billionaires, they needed to be good at running a business, inherit it, etc. Which doesn’t correlate to being a great investor.
So when you actually look at investments made by billionaires they tend to underperform. Part of this is simply seeking low risk diversification, but another part is many people assuming that because past risk taking worked so will future risk taking.
This becomes really obvious when you start looking into former billionaires. Vast fortunes regularly evaporate.