It's not all games. It's one game. Just like the networks aren't bound to show every political debate, just the main presidential ones.
The NFL is also absolutely bound bound to show a big majority of its games for free. Once it moves to pay-per-view, it loses it's anti-trust exemption. The NFL realizes this, and even the spokesman this week acknowledged it.
The Sherman Antitrust Act of 1890 passed by Teddy Roosevelt went into effect to prevent groups such as the NFL from acting as monopolies. Effectively, if the Senators used the provisions of the bill against the NFL, they would force the NFL to break up into competing corporations, each team making its own sponsorship deal, and new teams seeking to start franchises would also have that opportunity.
The Sports Broadcast Act of 1961 is the one that establishes that groups such as the NFL that wish to retain their exemption must serve the public interest. The burden of proof for violating this criteria is not that hard to meet. It simply has to be shown that there is a public interest "rationale" that is being violated.