The ISBN is an international standard for cataloging books. Each country designates how that system will be implemented within its borders. In Canada and India, for example, ISBNs are free (but you have to live there).
Basically what we have here is a system in which other countries encourage writers to publish and sell their work. But in America the smaller you are, the more you pay. Why must individuals and small publishers pay up to 125 times what corporations pay?
Bowker doesn’t say. My research indicates the prices are based on the old database management system they had in place in 1967, when the ISBN was created and they first got the rights to sell them. At that time, much of the data entry work was done by hand, so it took almost as long to catalog one ISBN as it did to handle 1000. But I doubt they are using that system today. The MyIdentifiers web site (Bowker’s sales site) uses a web interface in which the purchaser enters all the info. Their computers do most of the work.