It's just "quality", and while it may be difficult to say whether it correlates better with the fun during creation than with sellability, the important thing is that quality doesn't correlated with sellability very much. There are way too many other inputs that influence whether or not people will buy something - like marketing, economies of scale and access to distribution.

(Though I'm pretty sure that this hypothetical Open Source McDonald's would exist. It, and other fast food joints, solve a legitimate consumer problem - getting hot and actually tasty food quickly.)