[nearbuy]

Star Wars almost feels a bit like it's public domain already. They've been pretty liberal with licensing their IP so we ended up with a huge number of Star Wars books, comics, games, LEGO sets, merchandise, etc. At the limit, there isn't much practical difference between a public domain work and an IP that will grant anyone a license for a very reasonable fee.

If Star Wars were public domain due to shorter copyright, the newer works and characters would still be protected. Another film studio could make a new movie based off the original trilogy, taking things in a different direction than the new movies. I'm not sure this is likely though, just like no one is rushing to make 3rd party Mickey Mouse cartoons since it entered the public domain. It probably changes things a lot less than copyright proponents worry about.

Even with books, which are much cheaper to produce than movies, the original author would probably capture most of the money from their works under shorter copyright (e.g. 25 year copyright). If you like a series from a particular author, you want new books from that author. You're not going to read A Game of Thrones and then continue with a sequel written by someone else. And as long as the author keeps writing, they're expanding the canonical world in their series with freshly copyrighted IP, and fans will primarily want new works that build on that.

And if an author writes a sequel so bad that fans abandon the series and someone else writes a better sequel that fans flock to... well, the world is better off. Even the original author may be better off if it improves the popularity of the series.