Comment by cbm-vic-20

[A]GPL is like kryptonite to corporations. Very few will take the risk of having to open their own code if someone made a mistake in isolating the GPLed code properly, so most ban the use of GPL for their products and services.

Anthropic would have found a different library or rolled their own, rather than taking that risk. If the library was fundamental, maybe they'd go for a commercial license, but that's usually an option of last resort.