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?
This is what a society looks like that isn’t run for the purpose of maximizing profit of companies.
The government doesn't require books to have ISBNs, so why should issuing them be the government's problem?
There's nothing to stop you from setting up your own, alternative book numbering system that nobody cares about if you think you can do a better job.
is it?
Trademarks and patents are enforced by governments. Unique identifiers for books was a marketing idea. You, me, anyone could create a new system and somebody probably will :)