»One goal of Creative Commons is to increase the amount of openly licensed creativity in “the commons” — the body of work freely available for legal use, sharing, repurposing, and remixing.« https://creativecommons.org/use-remix/ (on 4th of December 2016)
There are major successful projects like Wikipedia which use a CC license which allow sharing and building upon other's works.
If you build upon this text of Wikipedia and combine them and/or add you own text to them, it poses no major problems – at the end of the new text you put a link to the license. This will not bother anyone, for the declaration of license and contributors is usually a tiny part of the overall text length.
It gets more tricky with using images or other non textual data: The the license requriements of stating and linking are not as easy to meet there. Recently, a college of mine wanted to design a print for a shirt. For this, she wanted to use two creative commons images (CC-BY-SA). Problem: But how do we state the licenses? The minimal text size that could be still printed on a shirt was rather large and the draft with a logo and a significant part of not-so-fine-print (maybe a 5th of the graphic in size) did not fare very well, aesthetically. It was impractical to build upon these works, and we ended up creating our own graphics.
But this is just combining existing works to a new one. What about sharing a work so that others can change it easily? You can easily share the finished version of the artwork as an image, pdf or a mp3. But these are formats for works not being changed anymore. For creative work which goes beyond merely using or citing a work, you need the source. And sharing the source (-format) is more difficult.The larger platforms which index your file and allow others to find it (youtube, flickr, Wikimedia Commons) take few formats and usually these formats are meant for finished works. So you can create a poster in some layout application, but you can only upload a pdf. You can cut a video, but you can't use the editor’s format but need to upload the uneditable, rendered mpg. An exception is SVG which can be uploaded to Wikimedia commons and which is an editable format.
Since the original files are not available, building upon, changing and improving works is sometimes hard, sometimes impossible.
This does not only pose a problem for reuse and changes. It also makes learning more difficult. To see how a work has been created can be helpful: See how the creator organized its layers or tracks, see how parts play together and how interesting effects were created.
The problem of stating the license in a way that may be difficult to do depending on the media you use (T-Shirts?) is a legal one. As far as I remember, Creative Commons Licenses are vague by purpose to allow an appropriate style of attribution, however, I am unusally unsure if a rather liberal interpretation would be still in the limits.
The problem of providing editable files for the purpose of improvement and learning is largely technical, since possibilities to share the source files need to be provided to make it possible. However, it has a cultural component, too: Many artists and designers may be reluctant to share their works in a way that exposes all the seams and hacks, like the embarrisingly unorganized photoshop file with layer names like Next, TopOne and Nameless Layer. If it is too embarrasing or the social gain not high enough to clean it up, all technical foundations will not solve the issue.
Problems of using (non textual) Creative Commons-Licensed works for building upon them by Jan Dittrich is licensed under a Creative Commons Attribution 4.0 International License.