Unlike college football, which on any given Saturday has more than a dozen games airing on a variety of cable and over-the-air TV channels, the NFL is much more stingy with its broadcast distribution.
Unless you've got NFL Sunday Ticket—which requires you to be a DirecTV satellite subscriber—you're stuck with whatever games that CBS, Fox, NBC, ESPN and the NFL Network decide to show you.
It doesn't seem fair, but it's the way the NFL has done it for decades and it's not likely to change anytime soon. So rather than complain it's best to just be prepared for what's to come, which during the two Sunday daytime windows is dependent on where in the United States you live.