For one, the president has issued so many waivers and exemptions to political allies since the U.S. Supreme Court mistakenly upheld the law as constitutional that it figured he would do the same for Congress. And two, back in May, the leaders of both parties were caught negotiating in secret to find a way to exempt themselves from a law the Legislative Branch passed.
Granted, the decision to largely exempt lawmakers "officially" came from a "ruling" issued by the Office of Personnel Management. But the OPM is part of the federal bureaucracy, and the federal bureaucracy is managed by the Executive Branch, which is headed by the president. Plus, it's being reported that Obama personally intervened to ensure this "ruling" was issued.'