I would personally argue that as the amount of money and time required for distribution has gone down, the duration of copyright should also go down. 14+14 years was the first federal rule in the United States, and that was in an era where even electric telegraphs didn’t exist and it took several days just to send a letter 100 miles.

Actually, don’t even listen to me. In 2007, an economist named Rufus Pollock did research to determine the ‘optimal’ copyright duration to answer this question using empirically-estimable parameters and arrived at an optimum of 15 years.[0]

It is important to keep in mind that (1) copyright was supposed to promote the creation of new works, and so allowing creators to make a single hit and collect royalties until the end of time is not its purpose (at least in the United States), and (2) just because something is in the public domain doesn’t mean that the creator is now unable to make money from it.

Taking your example of the Song of Ice and Fire: if its copyright had expired before it exploded in popularity, George R.R. Martin would still be able to make money consulting for the TV adaptation. He would be able to make money giving talks and appearing at conventions. He would certainly increase the number of people giving him money on Patreon and sales of his contemporaneous books still under copyright would go up. He could cash in by quickly preparing some bonus content related to the book that is under copyright and sell it alone or as a bundle. He could do a fresh run of printed copies and tout their superior physical quality versus other copies on the market.

[0] https://rufuspollock.com/papers/optimal_copyright_term_talk_...

I'd like for something like 10-20 years after the creator's death -- but even then, that gets complicated because if the owner is a corporation, then that work will probably never enter the public domain.