Can anyone explain why exactly the BBC did the show development and production like this? It seems a little insane to pull everyone together for a pilot, that from all accounts went well, and then totally redo everything.
I don't think they released too many details, but there are several possible reasons that come to mind:
1 - Executive meddling. Probably the most likely, as network executives are known for their ability to try to "fix" stuff that isn't broken.
2 - Artistic direction. It could be that the creators decided they weren't entirely happy with the orgiinal. Reading between the lines, this may have happened with the original vampire - the interviews make it sound like the creator wasn't 100% happy with the original actor.
3 - The actors may have refused to sign a longer contract, maybe they got a better job in the time between the pilot's production and the series being picked up.
4 - The pilot was relatively popular, but there was clearly room for improvement. I agree with some of the comments made in the interviews about the changes - specifically, the pilot did seem to lack a bit of cohesiveness, and there were points that felt like the creators weren't entirely sure what direction the show was supposed to take. I think that one way or another, it was good that they decided, though I hope they made a good decision.