Part of it too I think is that the closer Red Dwarf gets to Earth I think the more remnants they find of humanity even thought they're extinct......or at least virtually extinct. However having people pulled through time is the laziest they've done so far. The best handling of this was in Samasra where they day before they even really get to interact with the Red Dwarf crew.....which was an interesting way to kick off the core plot, even if it was kinda a dull one! I mind far less when they interact with non-human characters they encounter, since they first started doing that with Kryten in series 2. However I think they really need to start dialling back the guest casts because in series XII it's starting to get more then a little ridiculous after 3 episodes in a row on it!