Researchers cease to cite article save for historical purposes.
There are very few books which are individually essential , and one of the tasks is that the producers of books all have to persuade the next people in the chain of production and distribution that their particular book is necessary and worth publishing. The publisher has to guess how many copies are likely to sell at the chosen price, and many factors can interfere with this. If he miscalculates a bit, some copies may go to remainder dealers to be sold at a lower price. If he has miscalculated very badly, thousands of unsaleable books have to be sent to be pulped and he loses a lot of money on them. These books will also frequently have been produced only in small editions, so that the unit costs per copy for their production were high.