There is no any other explanation why the rich who constitute a mare 10% of the population control 76% of the wealth, other than the retrogressive tax system in place. Low-income earners pay a higher percentage of tax while high-income earner pay very little, in this situation, the rich continue to be rich while the poor continue to languish in poverty.
The richest 10% hold 76% of the wealth in the United States, due in part to tax policies that favor the wealthy. Since the 1980s, there have been policies aimed to benefit the rich, such as cuts to the top tax rate, and lower rates on dividends and capital gains. This is being done instead of redistributing the wealth through a more progressive tax systems to fund programs.
The game is indeed rigged: wealthy people are able to get away with paying so few taxes that they can hold onto their riches and even have the ability to increase it. Therefore it isn't surprising that the wealthiest 10% control a whopping 76% of the world's money - it's because of tax policies that give them the advantage.
Part of what makes people wealthy (as opposed to being well off) is learning to use the existing tax system -- any system -- in the most favorable way. Our current tax code is favorable to the very poor, through refunds in excess of anything paid in. The middlin' poor (used to be called the middle class) is not favored at all: they earn a pay and spend the money buying mostly nondeductible necessities. The very rich can decide where to invest to retain the most income after taxes.