Perhaps, as the Washington Post's Ezra Klein theorizes, it's because you can shape it to match whatever other positions you're taking.
Think about what Republicans are pushing under the guise of deficit reduction: Privatizing Medicare. Lowering tax rates. Block-granting Medicaid. Repealing the Affordable Care Act and most of financial regulation. Capping spending as a percentage of GDP. The Democrats, meanwhile, have invoked the deficit to help pass, and, in the White House's debt-reduction framework, expand and entrench, a universal health-care system. In the Bush years, congressional Democrats wielded a prime argument against almost everything President Bush wanted to do. That's the thing about the deficit: It can be used in service of any policy, even those that increase deficits, like the permanent extension of the Bush tax cuts. It can also be used to oppose almost any policy, including those that reduce deficits, like the Affordable Care Act.