During an interview with Vulture at the Television Critics Association's summer press tour, Parks and Recreation's Retta revealed the real reason for the time-jump in the sitcom's sixth-season finale.
Surprisingly, it wasn't about the plot development at all, but rather, a specific request from Amy Poehler, says Retta:
I saw Amy Poehler at Aziz Ansari's birthday party and she was like, "I'm not working with babies, so I told them we're doing a time jump so I don't have to work with babies... I just had two kids. I've had my share of babies for the last three years. I'm not doing another year of babies. Especially triplets." ... So, that's why they changed it. [Vulture]
Retta also hopes that there will be more of Keegan-Michael Key's character, Joe, in the show's seventh season, which begins production August 11. Read the rest of the interview over at Vulture.