An article in the New York Times on President Obama's unsuccessful attempt to eliminate tax benefits for college savings accounts notes, "In theory, tax reform is supposed to be built around cutting back preferences like these, in order to pay for some combination of lower tax rates and tax preferences aimed at people with lower incomes." The writer concludes that in practice, tax reform is difficult to enact. Briefly explain why it may be difficult politically to eliminate tax preference for some groups in order to improve the efficiency of the tax code by reducing general tax rates.