Adding a game to the regular season is no big deal. The players make an insane amount of money, and the fans pay an insane amount of money for tickets to the games and merchandise. It all balances out.
I was friends with someone that was a former MLB player. He always claimed the NFL is fixed/predetermined. There are "storylines" the NFL likes to focus on, and certain players they like to draw attention to. There are billions of dollars being generated and they very closely control the outcomes to preserve their profitability.
I have never been one to get wrapped up in the teams and players. I watch the games purely for entertainment on Sunday afternoons. There are guys at work that will literally spend the entire day on Monday doing a full recap of the games and will discuss specific plays that occurred during certain points, who had the most yardage, most rushing, worst rushing, which players are long-time friends from school and which players hate each other, who gets along with their coaches, who doesn't blah blah blah. It's just too much.