Why do so few magic books have ISBN numbers? I use personal library software to track my growing collection of magic books and it wants to search using ISBN numbers. Major publishers in the art like Kaufman and Vanishing, Inc. do not seem to have ISBN numbers on the books they publish or do not put them on their books. Is there a reason for this?

ISBNs cost money. A single ISBN in the USA may cost $125.

If the books are not sold/distributed through mainstream channels which require ISBN, the publishers may not see any reason to pay extra for it.

Maybe. Hermetic generally does it. So does Magicana. Not saying someone who is putting out a pamphlet or lecture notes needs one, but expensive hardcover books from L and L, Kaufman, Lorayne, etc? Seems like a small cost, especially at $125.