Why? Walk into any bookstore and you'll find it's full of people who wrote books in exchange for money. Many of them might write anyway, but they wouldn't necessarily have written those exact same books, and it wouldn't have been possible to write so many if they hadn't been compensated for their work-- because artists have rents to pay. They need money for food and clothing, and there's nothing wrong with writing for pay because you need money to meet your basic needs.

I see this attitude a lot... that somehow Art is tainted by association with money. I can understand why people might think so, but it's not terribly rational, nor is it terribly practical. Think about all your favorite authors and if you can, ask them if they'd still be able to do what they do if they had to write for free.

Like OP said, nobody tells medical professionals, managers or other professions that doing their jobs solely for money is shitty. People just expect them to do their jobs in a competent fashion, with the requisite compensation. Why are writers singled out?