This is equally true of my work as a scientist, as a software engineer, as a poet (http://www.siduri.net/cindylooyou/index.html) and as a novelist (http://www.amazon.com/Darwins-Theorem-TJ-Radcliffe-ebook/dp/...).
The market value of what I create (science: moderate, software: very high, poetry: almost zero, novel: barely more than almost zero) has nothing at all to do with my enjoyment of the act of creation, which is extremely high in all cases.
Some of my work I do for free for various reasons of my own, but mostly you have to pay for it if you want to have it, and I get to say that because it's my work. I own it. I made it. I created it. I'm an arrogant prick and if you don't like that... too bad. Go rip off someone else's work. I'm making good money from the stuff people are willing to pay for, and having lots of fun with everything I do, and so the loss is all on the side of those who can't appreciate the value of my other work.
If you think you deserve the output of my creativity without paying me simply because I enjoy the act of creation, the problem is all on your side.
Presumably some employer pays you to do your work as a scientist and a software engineer, and in the absence of that incentive, you would not do identical work.
Furthermore, enjoyment that comes from creating art requires your more basic needs to be satisfied (food, shelter, sleep, health, etc.). We can't just pay artists nothing and expect them to enjoy their art they way they would if their basic needs were satisfied. How much art can you create if your stomach is empty, if you're worrying about being able to afford your child's healthcare, if you come back tired at 6 pm from your day job?