It's probably a single dev that made the decision, then moves onto something else. They (probably?) don't have the ability to just raise a recurring PO etc to easily pay you and don't care enough to worth through the paperwork.
If you had a paid licencing model they may have done it, or just found another lib/ wrote their own.
They are doing it as one book instead of splitting?
The art on the side is cool if they are actually doing that!
Edit: you posted this just before the instance crashed unfortunately 😕