Posting cc-nc is already problematic on social media.
I consider the Non-Commercial term a bit confusing or just unclear, hence the so-called gray area. I think the NC term is so extensive that it ends up refraining the use of an intellectual work whenever money is involved, even indirectly. That's why, I think, social media prefer royalty-free material because it allows them to place ads in the webpages to generate revenue more safely.
I personally make a distinction between making profit off the work
itself (e.g. I produce a free software and someone else takes it and charge it) and -- if I can explain well -- using the work as a mean or part of a process that produces the product to be sold or generate revenue (e.g. I produce a free software and someone uses it in a for-profit company or presents it in a for-profit medium). For example, you took a picture of a landscape and post it in a social medium, the picture itself is not being sold but the page where the picture was posted has ads which generate revenue for the company that maintains the medium. It seems fine, but when it comes down to game screenshots and game footages, oh dear, some copyright holders will probably get mad and lawsuits may ensue or they just take your page down. It might sound stupid but it happens a lot.
(Am I missing something? I'm not a license expert.)
Besides, if one day we decide to allow ads in our sites or social medias (we did it once, anyone remembers? o.o) to generate financial resources to maintain our sites, CC-BY is preferable. The name of the authors will never be removed, we will never sell the works themselves, but at least nobody will feel guilty.
