Music existed, but not recording devices, microphones etc. There is a hard cost associated with all of those. Granted, those costs have come down over time, but the rental of a decent studio is not $0.
The cost of studio rental is irrelevant. What musicians want to be compensated for is the lifetime of study, dedication to a craft, years of poverty and uncertainty, risk of repetitive stress injuries, etc.
"And they do, whenever they perform those skills for an audience. "
The overwhelming majority of musical work -writing, recording, practicing etc - is done in private with no audience present. Many musicians perform very little in public.
That doesn't mean the market values such effort. They have no right to demand to be paid just because something takes skill. Lots of skilled activities are of no value to the market. And I say this as a musician who's very aware of the effort involved.
Not necessarily. They can of course charge before demonstrating said skill, but if someone else happens to be witness, or copy the output in some way, it doesn't mean he controls all future uses of the result of said skill.
"The market doesn't pay for effort, it pays for things people want."
The problem is that people still want the the product as much as they ever did, but they've discovered that they can always get it without paying a penny. The producer produces and the consumer consumes but the producer is not compensated. That's not a market.
