You also need to consider overlap of investments with the main source of income. For Bezos, it makes no sense to just buy a NASDAQ ETF since most of his wealth

You also need to consider overlap of investments with the main source of income. For Bezos, it makes no sense to just buy a NASDAQ ETF since most of his wealth is already highly correlated with it. Either he hedges this effect out or skews investments otherwise. In either case he'll need knowledgeable people that can plan the effects on both financial and tax side. That's also a likely reason why family office holdings often look very odd as they often only provide a hedge in case the main source of income dries up. And therefore, they cannot have any connection with it. Pure performance on a standalone basis is often only second priority.