One Can Only Wonder...

There are four main voice actresses in My Little Pony: Friendship is Magic.  Tara Strong is Twilight Sparkle; Ashleigh Ball is Applejack and Rainbow Dash; Andrea Libman is Pinkie Pie and Fluttershy; and Tabitha St. Germain is Rarity and several recurring characters (notably Grannie Smith, Zecora, and Princess Luna).

Andrea  Libman has had almost no appearances in the last two episodes - Pinkie Pie had four lines in "The Cutie Pox", but that was it.  Fluttershy hasn't appeared at all.

Ashleigh Ball has had somewhat better luck, as Applejack has played major roles in both "Sisterhooves Social" and "The Cutie Pox", but Rainbow Dash hasn't done much lately.

Tabitha St. Germain, on the other hand, has had the spotlight lately.  Rarity was cut from "Luna Eclipsed" after storyboards, but Zecora played a large role, Grannie Smith showed up for the first time in ages (with a line, no less), and of course, Luna was the centerpiece.  Rarity was one of the main characters in "Sisterhooves Social" (and she's getting another episode later this season), with another Grannie Smith scene as well.  And Zecora was again a major part of the episode in "The Cutie Pox" (with yet another Grannie Smith scene).

Did she have a word with the producers?

(It's worth noting that technically, there are five major voice actresses in MLP - Cathy Weseluck voices Spike.  But it's a little hard to class her alongside the Mane Six voices.)