The way I see it, Haruhi "had" to recruit certain people--Kyon just because he's important to her, Yuki since she was already there, Mikuru as the mascot, Itsuki as the mysterious transfer student. They were appealing and at the time she had a need to attract people to the club. After that, however, I think she just has the idea that people should volunteer to join, and/or isn't the mindset of thinking "this is a person who should join" plus hasn't seen many more people who qualify as that.
Spoiler for Volume 7 (Intrigues):
The "anti-SOS" won't exist in the sense that it would be like an evil brigade, it will just consist of new characters from various factions that are being introduced in furtherment of Tanigawa's incredible plots. I can't imagine there could ever be an equivalent of Kyon--as I see it, the characters will probably always just Kyon, his unknowing friends and the unknowing Haruhi, and his fellow SOS Brigade conspirators and all their troublesome conspiracies.
From Editor in Chief (up to where it's translated now, at 75%):
Same with how Mori, the butler and the two brothers from the Organization played a major role in chapter 6 of Intrigues. The story's plot is branching out from just the SOS Brigade + Kyon's sister & friends + Tsuruya-as-just-an-unusual-senpai + Asahana-san (big) + time-traveling and sliding around to resolve various paranormal occurrences, into a story involving various characters and plots and unexpected twists that convey a much more heavy sense than "here we go again" (in fact, the typical "let's be concerned about Haruhi" storylines are not just less present arbitrarily, it's justified as Haruhi having "stabilized"). It's a general shift in the story, which allows us to focus on various characters, not just Haruhi (who is being developed a lot in recent chapters I've noticed, even if the major plot focus appears to be some other characters like Yuki or Mikuru) and their problems and allow both them and Kyon to mature in the face of different and difficult situations in a serious manner, rather than centering around creating a specific set of villains in a certain manner. That's IMO.