If those cultists bother him that much, can't he just parasitize them!? Like those "grass" members he created before!? And whats stopping him from doing that to the queen herself!?
@Wick The queen might have skills or resistances that prevent him from doing so. Such existing has been mentioned earlier.
The loopy cultists -dunno. Maybe the princess asked him not to do that to her people if they weren't active enemies? And she can't read his mind, so no idea why he wouldn't do it anyway.