That's largely because the fight for primacy between continental authorities and national ones is still ongoing. Unlike the US, where (beyond the occasional tactical posture) Congress, Presidency, and Supreme Court, have long been established as fundamentally supreme to their equivalent in local states, for the EU this has not yet been the case in many areas. Even the courts of one of the pillars of the union, Germany, recently refused to certify such primacy, and are currently in the process of being sanctioned.