There's an obvious reason to treat the work of an author and a furniture builder differently, and that's in how they get paid.
- I bake you a bread, build you a chair, mow your lawn, teach you how to knit -- I do a job for you, you pay me for it, I get enough from you to cover my expenses and get a decent wage. We're done.
- I hold a concert -- I do a job for a lot of people, all of them pay me a part of the total cost, and all together, I get enough to cover my expenses and have a decent wage. We're done.
- But: If I write a book, or make a computer game, or design a new type of chair, I need a lot of people to each pay a part of the total cost, the payments will be spread out over time (unlike the concert), and I'm vulnerable because someone else could copy my work in a fraction of the time I spent, sell it much cheaper, and rob me of the fruits of my labor. So we need laws and cultural norms to protect the creators' rights in these cases.
Life + (small amount of time) will be enough to protect the creators' wages, eternal copyright gives no advantages to society, and a lot of disadvantages that have been described in this thread.