That reason has nothing to do with intellectual property or how it's created, it's a consequence of living in a capitalist society.
So, yes, capitalism in the sense of the freedom to trade one's labor does appear to be naturally and universally emergent in advanced human societies, in the absence of violent interference.
To the extent that certain aspects of capitalism lead to violence, those are elements that other parties -- generally corporations or governments rather than writers or philosophers -- added to the ideology.
People die trying to break out of non-capitalist countries, while they die trying to break in to capitalist ones. That's one possible way to tell the good guys from the bad guys.
Ahahah, I absolutely love this sentence. You might have said the quiet part out loud though.
“You gots to understand”, said Fat Tony, “I'm not a violent man. The violence simply comes in when you interfere with my business.”
But capitalism prevails and may be the best system there is for now because I cannot fathom a change in system overnight that would not result in mass suffering for (almost) everyone.
Can you point to a system that worked well before that you'd like to go back to?
I just wanted to point out that capitalism is in fact a specific economic system. It's not a law of nature, or another word for "markets" or "freedom", or a realization that some other system doesn't work.
If all artists are "weekend warriors", they will still produce a lot of art, and some of it will be the best in that world. But the quality will be far from what we enjoy today.
That said, there are of course other ways to pay artists than the capitalist way of having customers pay for what they like. But I think the track record firmly favors a capitalist system.
Then came the brutal reality: creating high-quality artwork needs time. Some can be created after work, but not that much. Some forms of art require expensive instruments. Some, like filmmaking, require collaboration and coordination of many people. So yes, I could do some forms of art part-time using the money from my day job, but I knew it was a far cry from what I could do when working on it full time. It's not capitalism, it's just reality.