The richest stay the quietest
In merchant societies the wealthiest families are often the most discreet. Their wealth is hard to see from outside, so outward display is a poor guide to who actually holds the money.
Business
Fortunes need luck plus effort
Great family trading fortunes come from luck, talent and hard work together, not from any one of them alone. Being in the right place at the right time pays off only for families able and willing to work the opening.
Rulers leave merchant profits alone
Where rulers depend on a trading class, they seldom do anything that would seriously interfere with the merchants' pursuit of profit. The ruler holds political power and the merchants run commerce, and each side keeps out of the other's core business.