I don't know why. Amazon is just as good looking up the title.... as is google. With the title, often you get the author's website. I don't think it would come up so readily with simply the ISBN. Besides, this author has penned many books. I think I need another copy for my lending library.
I am delighted that there is more interest in this item. It is encouraging that people are seeking out this particular, simple wisdom. However, it means more competion for me, which is somewhat disconserting. Thanks for offering it to the community. I wish you the best of luck on all your auctions.
Maybe they want the isbn to see if a book is collectible, or first edition... That's the only reason I could think of to want it. That's about the only thing you can find out about a book that you can't find out using the title.