One reason for the Vincent Price book not being indexed yet (as with New Doubleday Cookbook and a number of others on 100+ members' bookshelves) is that it contains so many recipes -- close to 1000. That means it will take as much indexer time as four or five typical new cookbooks.
Another factor is the count of Requests to Index -- a book that's on many members' shelves but has only a few requests will fall behind one with many requests to index in the EYB indexing queue, even if the more-requested one is on fewer bookshelves.
A big book, like the Price or Doubleday, is going to need a real spike in requests to index to overcome the hurdle of extra size. A similar but even more intense problem is posed by one of the great books of classical French cooking, the Escoffier Cookbook: on almost 300 bookshelves -- but with a daunting 3000 recipes. Back in the early days of Member Indexing, an edition of Larousse Gastronomique, with close to 4000 recipes, was EYB indexed -- and I note that very few members have it on their shelves. (It's on mine, because my parents bought it as part of a hard-to-resist book club deal in the 1960s.) Possibly that unrewarding experience has colored the approach to other big but little-requested tomes.