Some, and maybe most, of the complexity is organic. But there are specific instances, like the tax code, that have been kept intentionally complex at the beques

Some, and maybe most, of the complexity is organic. But there are specific instances, like the tax code, that have been kept intentionally complex at the bequest of special interest groups. And of course, laws are made mostly by lawyers. So they don't have much of an incentive to change things.