PG-13 Movies are allowed a maximum of 1 non-sexualized use of the f-bomb per movie.

Here's an article referencing this rule.

As for why both f-words were bleeped out rather then the one required for the PG-13 rating, it would be strange stylistically to bleep out one f-word and leave another in the same scene unbleeped.

PG-13 Movies are generally allowed a maximum of 1 non-sexualized use of the f-bomb per movie. There can be exceptions to this rule.

From the Daily Mail:

Officially, the MPAA's Classification and Ratings Administration's guidelines state: 'A motion picture's single use of one of the harsher sexually-derived words, though only as an expletive, initially requires at least a PG-13 rating. More than one such expletive requires an R rating, as must even one of those words used in a sexual context. The MPAA's guidelines state that if two-thirds of the ratings board members believe that multiple F-words are used in a legitimate 'context or manner' or are 'inconspicuous,' then the movie could still be rated PG-13.

As for why both f-words were bleeped out rather then the one required for the PG-13 rating, it would be strange stylistically to bleep out one f-word and leave another in the same scene unbleeped. Hunger Games was able to use the in-universe TV show as an excuse to bleep profanity.

PG-13 Movies are allowed a maximum of 1 non-sexualized use of the f-bomb per movie.

Here's an article referencing this rule.

PG-13 Movies are allowed a maximum of 1 non-sexualized use of the f-bomb per movie.

Here's an article referencing this rule.

As for why both f-words were bleeped out rather then the one required for the PG-13 rating, it would be strange stylistically to bleep out one f-word and leave another in the same scene unbleeped.