Most people in a crowd don't contribute. When we think of Wikipedia, a stunning demonstration of the power of crowds, we tend to imagine millions of people working on it in the wee hours of the morning. In fact, most of the work was done by just 5,000 people.
The power of crowdsourcing is not that lots of people will make great contributions, it's that we don't have to pick the best contributors beforehand. They can now pick themselves. And that's useful because it's hard to know beforehand who's going to be any good.
The internet has enabled writers, artists, musicians, and filmmakers to distribute their work to the whole world for free with the press of a button. The floodgates have been opened. Most of what comes through won't be any good. But the best will be better than what got through in the closed, curated model.