I'm not too surprised, I have a feeling there isn't a huge fanbase that would be looking a continuation, at least outside of England, so a reboot is probably way to draw in more audience. For a continuation to work it seems to me like you really need a big continuing audience who is going have held interest in the story since the original ended, and I don't know if Blake's 7 has that.At this year's Gallifrey One convention, I had the chance to ask Jason Haigh-Ellery about the Blake's 7 reboot. He's involved with the new series. There isn't much he could say in these early days but he did say that his main role was interacting with the Nation Estate.
He also confirmed that it is a reboot rather than a continuation. That's not really surprising but nice to confirm.

