I think it's mostly because of the kind of legalese used in the license text, as they are designed for art.
From their FAQ:
> Can I apply a Creative Commons license to software?
> We recommend against using Creative Commons licenses for software. Instead, we strongly encourage you to use one of the very good software licenses which are already available. (...)
> Unlike software-specific licenses, CC licenses do not contain specific terms about the distribution of source code, which is often important to ensuring the free reuse and modifiability of software. (...)
From their FAQ:
> Can I apply a Creative Commons license to software?
> We recommend against using Creative Commons licenses for software. Instead, we strongly encourage you to use one of the very good software licenses which are already available. (...)
> Unlike software-specific licenses, CC licenses do not contain specific terms about the distribution of source code, which is often important to ensuring the free reuse and modifiability of software. (...)
https://creativecommons.org/faq/#can-i-apply-a-creative-comm...