For a work like this where years of research and compilation have gone into it it could only benefit from going with an established publisher. That said I might see a significant hurdle in wanting/needing the volume of work presented in three separate volumes. I admit a publisher might have a problem committing to an 1800 page reference book about a popular television series with a nontheless cultish like following. And they mightn't be willing to consider taking a chance on three separate volumes when the first alone might not sell in sufficiently large numbers.
As such we are left with the work as is, which regrettably just isn't good enough for some. It's an open question as to how many potential sales are being lost because of some sloppy errors.