Apparently, this company has the sole right to issue ISBNs; no other company in the USA is legally allowed to do so. This is highly unusual, since it is a for-profit corporation, not a government agency. So I must be missing something—why is this possible?
Imagine if the government required car license plates, but instead of issuing them itself or through its affiliates, there was a parasitic middleman that the government required you to buy from. I know ICANN is somewhat similar, but ICANN is effectively a child of a U.S. defense agency, so it makes sense—and you can buy domains from multiple companies.
Why isn’t ISBN funded and run by a government agency, like the U.S. Trademark Office?
ISBNs are not legally required by the government, any more than a book is required to have a title. They are a convenience for getting a book out there in retail channels and have it be identifiable, trackable, etc.
Any other person or group is free to invent a new system and get everyone in the book industry to adopt it alongside or as a replacement for ISBNs.
The U.S. government is not making you get an ISBN for your book. Many books are published without one. But neither did the U.S. government step up in 1970 and offer to be the issuer, unlike in many other countries like India and Canada. So the U.S. is in the minority of countries where a for-profit company ended up getting the right to be the issuer for that country. Considering that the vast majority of books in the U.S. are published by huge for-profit publishers, it doesn't seem that bad to have them pay the issuer $30 for a ISBN if they want the convenience. It's a free country, so they are free to eschew the ISBN as well.
I guess if you feel so strongly about it, you can lobby Congress to buy out R.R. Bowker, make the Librarian of Congress the registrar offering ISBNs for free, so they can add to the so-called Deep State!