Dennis Karjala was a law professor who helped lead the doomed resistance to the 1998 extension. He passed away in 2017, but when I interviewed him in 2013, he told me that it was "basically the Gershwin family trust, grandchildren of Oscar Hammerstein, Disney, others of that ilk" who pushed for ever-longer copyright terms.
Most copyrighted works become commercially worthless within a decade or two. But a small minority of famous works from the 1920s and 1930s were still generating significant revenues in the 1990s. Retroactively extending copyright terms meant an enormous windfall for the companies and families that owned the copyrights.
"There was not a single argument that actually can stand up to any kind of reasonable analysis," Karjala said. But the public domain had few defenders. So even though the arguments for longer copyright terms weren't very strong, they won the day in Congress.
Until recently, I assumed that the same interest groups would try to extend copyright terms again in 2018. But the political climate for copyright legislation has changed radically over the last 20 years.
A year ago, Ars Technica broke the news that three of the nation's most powerful rights holder groups in the country, the Motion Picture Association of America, the Recording Industry Association of America, and the Authors Guild, were not even going to try to pass legislation extending copyrights...
That means that whereas thirty years ago probably very little of the early jazz era, and by early jazz era I'm going to say ragtime in its entirety, was public domain you could go to IMSLP and find almost everything Scott Joplin, James Scott, and Joseph Lamb published and be likely to find a sold pdf copy of any given score. You can't fully understand or appreciate what jazz emerged from if you don't understand ragtime. It's one of my hobby horses, I admit, and I've been playing with fusions of ragtime and sonata forms over the last few years because it's been a goal all my adult life to develop such a fusion.
Unlike a few people I've known over the years I didn't see the "Blurred Lines" verdict as bad. What those people who regard it as a terrible verdict may be vexed by is a fear that a genre can be copyrighted. That's an absurd claim since nobody would say ragtime is a copyrighted genre. You can do whatever you want with James Scott's "Modesty Rag" by now! The problem only emerges if you want to emulate a genre where everything is still under copyright because your listening habits are so entrenched in your near lifetime you don't dig any music that's already long-since passed into the public domain. That is most likely your real problem. I'm happy to mess with riffs from Reicha woodwind quintets or guitar sonatas by Matiegka and works by ragtime composers. I would suggest that while there are those musicians and fans of music who wish they could sample stuff from the 1940s on out that time isn't here yet. But what you could do is trawl through IMSLP for all the public domain works you can find, set up a gigantic midi library based on that, base it around an educational institution, and then make all those midi files up for free use.
If memory serves, I remember Ethan Hein proposing something like this at his blog, noting that the majority of classical music is public domain but that most recordings of that music are not public domain. Very true.
I've thought about writing more lately, or even this weekend, but I've got some offline projects I'm tackling.