I think you mean CC-BY-NC-SA 4.0 not CC-BY-NO-SA 4.0 and as far as I know it is intentional. All licenses allow for commercial use on here which is why it was excluded. I don't think many people would be interested in assets that didn't allow for commercial use.

It isn't so much about "we love commercial ventures! Yay capitalism!" The reason CC-BY-NC-* and CC-BY-ND-* licenses are not permitted here is because, despite the intent of the licenses, those provisions make it nearly impossible to legally use art in a game, commercial or not. Yes, that's right; even a non-commercial game would find it very difficult to legally use art licensed -NC. 

Which leads to your next point. GPL does indeed make it difficult to make money since you have to provide the source. There are 3 reasons GPL is a better fit here than -NC though:

1. being technically able to steal a game and legally able to steal a game are two different things. Can people compile the game themselves without paying for it since they have the source? Probably, but that doesn't make it legal for them to do so. 
2. It isn't really about being able to make money, or commercial ventrues. It's more about if the license allows people to use art in a game, regardless of commercial status. -NC really dosn't, but GPL does despite the open source provision. It's weird and stupid, but that's how the law works sometimes, unfortunately; the best intentions have unintended technicalities.
3. GPL isn't a very good license for art in the first place. It isn't intended for art at all. It's intended for code. However, there was game art being shared before Creative Commons licenses even existed. That art needed some license to allow it to be shared, so GPL was the best choice at the time. GPL is allowed here (despite not being an art license) for primarily legacy reasons. I would encourage artists NOT to use GPL for their work, but a lot of older assets were licensed GPL before we came along, and not supporting that license would mean those assets would not be preserved for future generations to enjoy. This reason doesn't exist for the -NC license.

Any license considered "Free" or "Open" by the Free Software Foundation and Open Source Initiative respectively must allow commercial redistribution. -NC and -ND licenses are not free nor open. See also:

• https://opengameart.org/forumtopic/oga-licensing-suggestion#comment-25213
• http://esr.ibiblio.org/?p=4559

I guess I'm not clear what your last two points are.

Was it that GPL code can't legally be compiled? That's not true. You can't legally compile it without making the source available, but outlawing the compilation of code would render any code you apply the license to effectively pointless.

Was your point that code and art can be licensed separately? I agree. Art can even be licensed GPL with the code licensed CC-BY. That doesn't really change the situation. Art licensed GPL is still accepted here because of legacy GPL art, but licensing art as GPL is typically not the best license choice. I also agree that GPL is in the free software category, which reenforces my point about GPL being a sub-par license choice for artwork. Is artwork software? If not, why apply a "free software" license to it? 

P.S. Please do not feel like this is an attack on your license choices. We feel artists can and should license their work under whatever conditions they choose. CC-BY-NC-SA is a completely valid license choice and you should not be made to feel bad for using it. We just can't use it here on OGA. Welcome to the community and I hope you're able to find some useful stuff here. :)

Understood. Your questions didn't seem rude to me. I just didn't understand what you were asking. You have clarified them, and I understand them now.

1. Because the terms in the -NC license are poorly defined or ambiguous, it is almost impossible to tell what would constitute "commercial use". For example: Let's say someone used art under the -NC license in their game, then posted that game here on OGA. (we don't really host games, but for the sake of this example, lets say OGA does.) Then, OGA decides to have advertisements to pay for hosting costs. Is that game breaking the law? OGA is technically making money by having that game hosted on the website. OGA takes donations currently. Is that breaking the law then? Since money is being made based on the content of the website, and that content is licensed Non-Commercial, is that going against the license? This is a rather extreme example, but not an unreasonable one because the -NC provisions don't really have a lot of limits outlined.
2. Ah, I see. No no no. I was not saying GPL code could not be compiled legally. I was saying it is possible to have a commercial game licensed GPL. It would be easy to steal the game, but it would still be stealing and illegal to do so. The fact that GPL does allow for commercial use is why the FSF and OSI consider GPL to be open and free, but do not consider -NC licenses to be open or free.