It comes from the Copyright Act: 17 USC 102 states that copyright protects "original works of authorship fixed in any tangible medium of expression." It also states that in "no case does copyright protection for an original work of authorship extend to any idea, procedure, process, system, method of operation, concept, principle, or discovery, regardless of the form in which it is described, explained, illustrated, or embodied in such work."
The way this has been interpreted is as a dichotomy between ideas/facts and expression. You might use very expensive equipment to, for example, map the ocean floor. That data cannot be copyrighted. But a video visualization of that data could be copyrighted.
The result is, as you point out, somewhat unintuitive in that case, since generating the data is the hard part, not creating the visualization. But that's where Congress chose to draw the line in order to circumscribe the scope of copyright.