The reason is that there is not a single entity called the “Creative Commons license.” Rather, Creative Commons offers a number of different licenses that can apply some rights and protections to your work, including the CC-BY and CC-BY-SA licenses which reflect open source values closely. [...]
Creative Commons also offers licenses that carry restrictions — against commercial use and/or derivative works — that are strictly incompatible with open source. The open source hardware definition states that a license for open source hardware “[...] shall allow for the manufacture, sale, distribution, and use of products created from the design files, the design files themselves, and derivatives thereof.” Thus, if you choose to release hardware under the banner of “open source,” that means that you agree to allow others to use your design commercially, as well as to create derivative works (and to use them commercially). Consequently, you cannot advertise your project or product as “open source” if it carries restrictions against either of those uses.
Image CC-BY creativecommons.org.