Good question! My answer: The world can't use young and hungry interns for everything. People will sometimes want or need people with experience and a proven track record. Having those, we may value and price ourselves accordingly. And working for less shows we lack respect for our own hard-earned skill and wisdom.
True story: A friend said she would pay me to read her book manuscript and honestly tell her why I think publishers won't accept it. I said I would, for $75 an hour. She said "That's too much," and ended the conversation. Another writer agreed to assess that manuscript free, as a friendship favor. Two years later that writer still has the manuscript and my friend hasn't heard a word. It's strained their friendship: My friend tries not to feel resentful and both of them try never to mention it. Big bargain, eh?
I'm not saying, apply at Wal-Mart and demand $40 an hour just because you've been in the work force for a while. I am saying, if you have decades of writing experience and are asked to provide a writing-related service, ask for money. Yes, it's hard to do, and it's hard to be cold-shouldered or to hear cluck-clucking about how uppity you are. But you should feel GOOD when someone is miffed because you won't work for little or nothing. Watch this eye-opening 3-minute clip on YouTube called "Pay the Writer" to see the sheer absurdity of abasing yourself and your entire profession.
We got ourselves into the "Sure, I'll work for nothing" trap, and have to get ourselves out. It won't be quick or easy. Do it anyway. Asking for fair wages for your work will help all the others who are too weak to ask.
I know that talking about our paychecks is the last taboo. Ever wonder who made it and keeps it taboo?