Voters are suspicious of both Democrats and Republicans, but the lingering delusion that they, too, might someday be wealthy tilts their apathy slightly in favor the rich - and that bait-and-switch known as "tax cuts". Meanwhile, corporate wealth gets candidates elected, which induces an ethical obligation to return the favor. The synergy of these two effects allows corporate interests to dominate Congress. This is why we have the persistently inequitable tax structure that we do. Read about the self-perpetuating engine of Wealth & Power at the links below.

"Why the rich get the most tax goodies" from the Christian Science Monitor
The Conservative Nanny State: How the Wealthy Use the Government to Stay Rich and Get Richer by Dean Baker