See if anyone else in the game dev community has experienced this kind of thing before. If it turns out to be a consistent problem then you could try to get a games journalist involved and see if they will write a story. In order to get anything done about it, you have to make enough noise that it comes to the attention of the people who can actually effect a change.

I’m not sure what the solution is though, because when the base concept is already in the public domain, it’s probably something that happens sometimes through pure coincidence. Like the ant movies. Steam would have to have a set of criteria by which they judge if someone is doing it deliberately and maliciously in order to classify it as fraud or impersonation. If it’s a big enough problem and happens regularly, maybe they would consider it though.