Why plagiarize where there is no profit?

I am a professional, published writer and a semi-professional digital artist. Over the years, Internet searches have shown that my work has been appropriated many, many times by people who post or publish it online under their own names. I don’t really mind, but I am baffled by why anyone would want to do this.

These people are not making a profit from republishing one of my stories or pictures, and even if they receive praise, they know that they had nothing to do with the creation of the work which is receiving the praise. What could they possibly be gaining from their appropriation of work not their own?

(What does irk me is when people plagiarizing me edit my picture to resize it or crop it, presumably in an attempt to hide my name or avoid hash detection, which results in a blurry, pixellated, and otherwise adulterated version of my work. Similarly, I’ve had people insert a horribly-written paragraph or two into a story I’ve written to add more explicit sexual content or change the ending to something trite and hackneyed.)