So the article is saying since the income of rich people can fluctuate by millions of dollars each year, the amount of taxes they pay also fluctuates by large amounts, and that makes budgeting hard. The solution is to instead tax the average person. Budgeting is easy since they make the same every year and so the tax collected will always be the same.

Do rich people think we’re idiots? This reads like Tom Sawyer convincing his friends to paint the fence for him.