I think it’s like this.

In the beginning, there are only a few submissions. They all are pretty different so people think they’re original and upvote them all.

After that, as more submissions come in, what was once unique is now buried in a sea of similar comments. When people see them now, they think they’re just another generic submission and downvote it, while the actually good ones continue to get upvoted. I’ve had one submission go up to +12 before dropping to -5 while others who were doing well before are now struggling.