After spending all this time, effort, and money honing our craft and developing a style amidst millions of photographers out there, I have no idea why anyone would let their work disappear into oblivion.
I don’t think most people would deliberately take credit for photos taken by others. Nor do I think most people ever have intensions of printing web images. But I have experienced having images reposted in other forums without my knowledge and having images show up in strangers’ blogs and having images passed around in chain emails. As long as my watermark is on the images I want to be associated with, I consider it free advertising, more or less, as long as there remains a way for interested parties to find me.
Since most people do not consider what they’re doing illegal nor immoral, they don’t take the time and effort to clone out watermarks.