It could be because the top 10 percent earn 76 percent of the income in the U.S., while the remaining 90 percent of the population gets to share the 24 percent left over that trickles down.

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https://usafacts.org/articles/who-pays-the-most-income-tax/#:~:text=If%20you%20include%20the%20top%2010%25%20%E2%80%94%20everyone,to%20%241.7%20trillion%2C%20or%2076%25%20of%20the%20total.