These files represent years of unpaid-for access to other people’s work, and artists have pushed back on past leaks for exactly that reason.

Not at all? All the artists are saying leaking Avatar early robbed it of a big exciting release, which apparently means a lot to them. If the production footage were released would they get royalties? From a web search it seems they dont even get it for the finished work. So the only party who is “unpaid-for” is Cartoon Network corporate. Weird pro-copyright lie from Mashable