The US still restricts the export of (some) cryptography to (some) countries & organizations. Mostly that just requires submitting a self-classification report to the BIS stating that the cryptography is "mass market" and matches the definition thereof in the export regulations.
The issue here is the complexity of complying and closing all loopholes that would allow the government to bring the full weight of the legal system against a library writer.
You don't understand the legal liabilities people open themselves to if they provide the software.
Now they have to fully KYC customers to make sure they are from the US, with US only storage, and firewall so that people travelling cannot use the encryption library from out of the US.
You've seen the lawsuits on just P2P link providers, this is even worse.