I wonder when they knew that Bloodlines was going to be replaced. The first year was pretty rough so maybe they knew the writing was on the wall but chose to let it limp along for two seasons anyways. Logistically, Knott's replaces two houses per year, and they originally probably expected that house to last a while, so they probably had to pull forward that replacement and design a new one for that space instead of replacing an older one.
Since HHN manages to design ten houses a year, it makes me curious as to whether they have a few plans in advance or just basic concepts that they design as soon as they need to.