I'm frankly surprised that so many on this board are unaware of cross-flexing games across networks. It's been around for three seasons. This is why the Eagles game was on CBS -- so more people could see it on a CBS doubleheader day:
"Beginning in 2014, the NFL will also be able to "cross-flex" games between Fox and CBS, enabling CBS to televise NFC away games (including NFC vs. NFC contests), and Fox to broadcast AFC away games (including AFC vs. AFC contests).
[28][29] The league can also "cross-flex" some of these games before the start of the season. For example, in
2014, the Carolina Panthers at Atlanta Falcons game in Week 17, originally a 1 PM Fox game, was cross-flexed to 4:25 PM on CBS. Despite the two teams' losing records, they were playing a game where the winner would become the NFC South champion and host a first-round playoff game. As Fox already had crucial NFC North games with playoff implications, and CBS did not have any games with such assigned to 4:25 PM (games with AFC playoff implications had been assigned to 1 PM), the NFL reassigned the game to CBS at 4:25 PM to give affiliates a game with playoff implications at the time."
https://en.wikipedia.org/wiki/National_Football_League_on_television#Flexible_scheduling