Blame the park for the decision, not the company who have taken the job.
We know Blackpool are cheap but they're kinda screwed with a retrack given Arrow's lack of real existence these days and that track being made in a time before full on CAD. Therefore a harder project.
Intamin from sounds of things were open but wanted to do all in one go (they're a busy manufacturer after all, and easier to put a full project through the workshop in one hit then annually in bits), but Thorpe have elected for the cheaper avenue.
As always, you pay what you get for. And the cheaper option doesn't always get you the product you were after.