Miles and Anna - why the *beep* not??

Why did they (the writers) have to be such miserable buggers and not have anna and miles end up together? It's what we all bloody wanted and it just feels like they kept them apart just to piss everyone off. It was forgiveable the first time because it left us all wanting more and at the time there was the possibility that there would be more but this was there one last chance and they still had to try and be too clever and 'unpredictable' for their own good. I really don't think that it would have been contrived for them to end up in a relationship, people who admit to loving each other generally atleast attempt to have a relationship and don't just shag four times over the course of 16 years!