It's because the Justice Department has been making ridiculous arguments about extra-constitutional federal powers that don't even get one vote at the Supreme Court. As I explain in the Wall Street Journal today:
The government's arguments across a wide variety of cases would essentially allow Congress and the executive branch to do whatever they wanted without meaningful constitutional restraint. This view is at odds with another unanimous Supreme Court decision, Bond v. United States (2011). Bond vindicated a criminal defendant's right to challenge the use of federal power to prosecute her. As Justice Kennedy wrote, "[F]ederalism protects the liberty of the individual from arbitrary power. When government acts in excess of its lawful powers, that liberty is at stake."
If the government loses in the health-care or immigration cases, it won't be because its lawyers had a bad day in court or because the justices ruled based on their political preferences. It will be because the Obama administration continues to make legal arguments that don't pass the smell test.