The original duration of copyright was a flat 14 years, with a single additional 14 year extension if the copyright holder applied for it. So 28 years in total.
It turns out that after 28 years the vast, vast majority of copyrighted works have already earned essentially all of the money that they will ever earn. Most of them go out of print forever before that point. It's only a rare few works that end up becoming "classics" and spawning "franchises" that last beyond that point. We're sacrificing the utility of the vast bulk of what should be in the public domain for the sake of making those occasional lucky hits into cash cows.
There's a great paper by Rufus Pollock, Forever Minus a Day? Calculating Optimal Copyright Term, wherein he uses rigorous economic analysis to calculate that the optimal duration of copyright for generating the maximum value for society is 15 years with a 99% confidence interval extending up to 38 years. So remarkably the original law hit the right duration almost exactly through sheer happenstance.
In an earlier paper he also determined that the optimal duration of copyright actually decreases as it becomes easier to distribute work, perhaps somewhat counterintuitively.
I'm good with going back to the original term of 14+14, as it strikes a good balance between providing incentive to create and opening older works up to the public domain.
Going back to this is where I would put it. If an artist cannot make new works after 28 years then maybe they just have to do other work. Most artists I know produce something about once a year or faster. Be it a song or a book or a painting.
The original duration of copyright was a flat 14 years, with a single additional 14 year extension if the copyright holder applied for it. So 28 years in total.
Just would like to qualify this with "in the US". Copyright law -- and IP law in general -- has varied around the world, and certainly back in (checks) 1790, when the original US copyright term was set, the world had not settled on a common duration. Today, the Berne Convention has done a lot to move things towards a common set of rules around the world, but that wasn't the case when the 14+14 term was around.
I'm American, but that does have significant impact, especially today and online, where to some degree places around the world are about-equally-accessible to each other.
If you see Europeans talking about "moral rights", for example, that's something that plays a more-significant role in copyright law in Europe than in the US.
Fair use is a US doctrine; while some countries have some level of analog, it isn't always available and may have different constraints and be considerably more-limited than in the US.
I was referring to the Statute of Anne, which was passed by the British parliament in 1710, which was 66 years before America declared independence. That's the actual "original copyright law".
The US copied it almost verbatim for their first copyright law, the Copyright Act of 1790, but that was 80 years later. The only change they made was to add maps and charts as things that could be copyrighted.