How did we arrive at life of author plus seventy years, or 95 years from publication for "authorless" works? You cannot simply say that my number is wrong - defend your own position.
As for my own, it is partially based on computer history. Ten-year-old software is old enough to be of minimal use for current productive work, but is still important for learning and for maintenance of historical hardware.
However, it is also based on cultural relevance. It's enough time for the original work to be commercially exhausted, but for further adaptations (eg. for music, samples or covers) to remain relevant. This is the approximate amount of time it takes for a series reboot to occur, or for a movie to be remade, if we want to keep it relevant to your particular field instead of mine.
But yes, the ten-year figure was rather arbitrary. I'd be happy with a twenty-year term as well. Just think, for your own use, what would be available. Imagine film students learning their craft by re-editing classics. Imagine films being translated and dubbed into any language with a speaker who cares enough to translate it. And instead of these things happening in the shadows, hushed up for fear of lawyers, it being done out in the open for all to see and benefit from.
Or, for your own benefit, imagine you could use any song over ten years old in your soundtrack? Go ahead, think of whatever song would be just *perfect* for whatever moment in whatever film you're currently working on - nine times out of ten, it will be out of copyright under a ten-year term.
How much profit do you think Return of the King is still making? The Last Samurai? Finding Nemo? What about the 2003 movies that weren't top-grossing already - say, 2 Fast 2 Furious, Dreamcatcher and The Room?
Let's go back to 1993 then - are Jurassic Park, Mrs. Doubtfire and Schindler's List still making much money? If we made those films absolutely free, would any of the people involved be noticeably affected? And those are from the top five highest-grossing films from that year, the ones most likely to have a long profitable period.
So it's a reasonable statement to claim that artists would not be seriously affected by a significantly reduced copyright, save for those that are coasting off work done decades ago and have done nothing worthwhile in a decade. And it's also reasonable to claim that a reduced copyright would drive creativity, by opening decades of masterpieces to new use. Remasters of old movies and songs will be ubiquitous, not something done only for the commercial cream-of-the-crop.
And what's more, True Art, capital A, has a message, something its creator wanted to say to the world. Reducing copyright lets that message be heard while it is still relevant - and is that not worth doing?