Perhaps a publishing by subscription scheme has not occurred before because a single title can take a long time to develop; so there is a tendency to think book by book. Only the most prolific authors could sell their works to the public by subscription, as Dickens did. But publishers have many authors; 20 or so should be enough to generate a constant supply of new product. And that makes it worthwhile for the public to subscribe.
Publishers are more like movie producers than movie directors. The mistake many early software companies made was to employ large numbers of programmers. Having to support a large payroll (and sometimes just greed) forced them to charge high prices for each copy of their software. Which led to piracy. Which led to copy protection and higher prices to make up for revenue lost to pirates. Which led to more piracy [41]. Software publishers eventually broke this cycle by abandoning copy protection and adopting a form of subscription publishing; successful publishers hooked their audience with a promise of continuous updates for a fee.
Instead of employing authors, the book publishing model is to encourage free-lance authors to write books, then help develop the projects, and promote and sell them. But publishers are more than mere intermediaries; the book industry would not exist at all without someone amortizing supply on one end and demand on the other, providing the capital and expertise to develop and edit titles, and getting titles from supply to demand. In many ways subscription publishing is the natural way to be a publisher--low unit margin but high and stable volume instead of high unit margin but low and unstable volume.
A large stable number of subscribers each paying a small amount per book is better than a few incidental buyers of expensive single copies. The uncertainty caused by emphasis on single copies is what is wrong with publishing as a business today. To those who argue that publishing should not be a business, the answer is that a large stable income frees publishers to produce quality books.