We barely pay creators as it is for generating copyrighted works. Nearly every copywritten work is available on the internet, for free, right now. And creators are still getting paid, albeit poorly, but that's a constant throughout history.
The thing about creators is that most of them are paid extremely poorly, and some of them get insanely rich. Joanne Rowling has received more money than a reasonable person could use for her wizard books, but millions of bloggers feeding much more data into AI training sets will never see a cent for their work. For starting authors selling books, this can easily be the difference between writing another book or giving up and taking up another job.
At the moment, there's also a huge difference between who does and who doesn't pay. If I put the HP collection on my website, you betcha Joanne Rowling's team is going to try to take it down. However, because OpenAI designed an AI system where content cannot be removed from its knowledge base and because their pockets are lined with cash for lawyers, it's practically free to violate whatever copyright rules it wants.
How does that favor a longer copyright? It’s not like these old works make a lot of money (with very few exceptions). And making money after 30 years is hardly a motivating factor.