Marach/Peya broke up earlier this year. (I found out because I was wondering why Peya was playing with Paes at the French Open.)
Zimo's playing with Janko at the Olympics (who, like Novak, probably wasn't willing to risk his prep for singles by doubling up, as it were). Llodra will be playing with Tsonga at the Olympics; the other pair France nominated was Benneteau/Gasquet, but you have Benneteau/Mahut here -- I would guess both Tsonga and Gasquet unavailable for the same reasons. (And Benneteau/Mahut made it to the finals at Bercy last year.)