Ideas cannot be copyrighted.
Yet the person who interprets the idea, puts enough words around it is granted a copyright. A claim of property is provided. This isn’t real property, it is intellectual property. Property that has, in this day, little cost of ownership, maybe less in creation.
The reason is lost to Queen Anne’s time.

Copyright is the fruit of the Patent Tree. It shouldn’t have been allowed to remain to rot. — hic scriptor