Because hooking up (even temporarily) the male and female leads of the show is one of the most boring and over-used plot devices that Hollyweird has, and it irritates me to no end. As soon as it was announced that Starbuck was going to be a woman, I knew that she and Apollo would get it on. Same thing with Adama Sr. and the President. Saw both of those coming from a mile away and the show didn't disappoint in delivering it.
Now, BSG is hardly the only transgressor in this matter. Stargate SG-1 is by far the worst for that in recent sci-fi shows, and I even like that show! It got so bad that I refuse to buy Season 8 on DVD, even if it means having an incomplete collection. I hope and pray that Stargate Atlantis (my other favourite show) doesn't follow that same well-trod path.