Because the vast majority loves them. To me it seems to be only a small minority group inside the hardcore fans that don't like them. When you look through comments on the web, you get far more "Why isn't there a spinoff series already" than "i never want to see them again".
Well people on this forum seem to have different tastes about the show than people on other forums and than I know in real life. Although I am in a minority here, from the rest of my whovian experience in life, you're probably all in a minority. But this is from my perspective. Still, from my viewpoint, this forum is the minority usually.
When I was your age, I remember that it was fairly easy to find people who hated stuff, far easier, in fact, than it was to find people who liked anything. Perhaps your experience is similar.
I have wondered more than once what the level of enthusiasm for a spin-off would be if it was Master Vastra and Jeremy and their relationship in the lead roles...
Pretty much. As i said, this is only my impression. One point, that is always to consider is, that the casual viewers would probably not comment on such specific details, they watch it when they like it and don't, when they don't. People that comment on such things are somewhat invested in the show and can be considered fans and as such the minority of the shows viewer-base.
Honestly, in terms of the people in real-life with whom I discuss DW and their views on its characters, only one recurring character ever provokes strong views: Jack Harkness. They may prefer Amy to Rose or Donna to Martha but its only online that I ever see people get worked up about any of them. Apart from Jack. One friend refuses to watch TW because of him.
I quite like them. Also, I've previously predicted that they'll make an appearance early in the 8th season in order to provide continuity with the new Doctor. Mr Awe
Unfortunately, I knew that was bound to happen. The biggest clue is Moffat referring to Capaldi's first series being like Tom Bakers, which had Jon Pertwee's recurring in the first serial; Sarah Jane and UNIT, so I guessed that we'd have a few episodes with the detective trio. Hopefully once Moffat leaves, the new producer will put the show back on track and ditch them. The Sontarans are like in the DW big five (Daleks, Cybermen, The Master, Sontarans and Weeping Angels), so having one as an ally really is a dumb thing to do. Plus it's so badly written. One thing I hate about DW in the last few years, especially in series 7 is that there is far too much humour in it. Crimson Horror is a prime example of this, and Dinosaurs on a Space Ship. Some people say that there's a dark side to Smith's doctor, but I really can't see that at all. They really need to sort out the show next year.