It's part of the larger trend IMO. I think it hasn't really been all that funny for the past couple seasons now. The newer characters (like Gabe or Kathy Bates's character) are just awful presences who suck all amusement out of the show, and many of the older ones are becoming stale (Dwight, Erin, Oscar, and Kevin only pop in and out of scenes to provide a few seconds of predictable, one-dimensional dialogue) or downright unlikeable (Pam and Jim are pretty much just smug shells of their former selves).
I don't know if the writers have changed or if they're just going through the motions now, but I don't know how much longer the show will last, given its current trajectory. I mean, how do you make Will Ferrell unfunny??? In hindsight, they probably should have just ended it with the wedding episode.