I'm not sure if the sharecropper analogy holds up. Sharecroppers essentially rent land, paying the landowner back with a share of the crops grown on it. Assuming the crop doesn't fail, both the cropper and the landowner make money.

On most web sites that aggregate user content, the content contributors make no money, and often the web site doesn't either (e.g. Wikipedia, YouTube, Facebook). These are more like online collaborative hobbies, where everyone involved is doing it just because they enjoy it and have some time to spare.