As animation, graphics, physics, and sound have become more advanced they've become a lot less flexible from a content creation standpoint (this is almost universally true of video games - and has been since almost the beginning). As the technology has improved the barrier for content creation has gone up... and up... and up... and the amount of resources it takes to match the quality of existing content has done nothing but increase. Most CC is terrible, some of it is mediocre, and a very small amount reaches the level of what get's published by professionals - and almost all of this CC lives in the land of scripts, or art that requires nothing from an animation or sound design. Some great things get made as CC, but a lot more great stuff that reached dev quality was possible when games as a medium were simpler.
