IIRC, the idea is to help the (dependents of the) Kurt Cobains of the world: artists who die young and still have loved ones who can now depend on the revenue from the copyrighted works for at least 20 years. But IANAL, so I could be way off.
Builders and doctors have regular salaries (or at least are paid in full upon completion of the work they do). The value of a creative work is in the income stream it creates over time. If you need the money now, you can recoup that by selling the rights. But it's hard to sell rights to an income stream that could disappear tomorrow if you were hit by a bus.
I'm pretty sure about 90% of professional creatives (artists, animators... programmers fall under almost all the criteria, too) are paid a salary as well. They work for DC, Disney, Amazon, etc. Tons working in either direct ad agencies or in the marketing departments of all kinds of business. All on a payroll.
Yeah, but they aren't who we're talking about here. That's called "work for hire" and it doesn't fall under an author's-life-plus-X-years rule. It has a fixed term.
Can you imagine the chaos if, every time someone died, everything they did for every company they worked for immediately fell into the public domain?
I agree. We as a society should have this discussion, no one wants their children to live in poverty and people, while they live, transfer their value to their children - so someone who dies early has missed the opportunity to do the same to their children. But, the fact that the Waltons exist is just stupid.