It might have been sold for a high price, but vellum and coloured inks were expensive at the time, and it is a very long document when a much shorter one would

It might have been sold for a high price, but vellum and coloured inks were expensive at the time, and it is a very long document when a much shorter one would still seem to fit the bill. Seems a bit of a gamble if that was the plan, and the scribes were presumably either well-to-do or trusted by someone well-to-do if they could get their hands on the raw materials. That makes the prank/con/crazy spirit writing theory seem less likely to me but certainly doesn't rule either out.