Alright, I will spell it out for you.
One of the excuses for copyright was that the author, having made a significant investment to create and distribute their work, need to be able to recoup their costs (and hopefully make a profit). Those sunk costs have plummeted.
But the main reason, which you don't seem to view as an answer, is that the current copyright terms do nothing except lock down culture and impoverish the public domain.
Now it's your turn to answer my question: how is life + 70 better for society than 15 years?