Probably just overlooked the memo from Obama about that…..
Check it out:

When asked to do so at a Thursday press briefing, Homeland Security Secretary Jeh Johnson failed to cite any law that authorized President Barack Obama to give Social Security Numbers to illegal aliens. asked Johnson: “A federal court in Texas v. United States has said giving an illegal alien a Social Security Number is not an act of prosecutorial discretion. What specific law gives the president the authority to give a Social Security Number to a foreign national in the country illegally?”