Useful here-say from some investors at the last few demo days: not all of the companies that are "copiers" apply + are accepted with the "copying" idea. Many founding teams end up pivoting during the batch and scramble to get proof points on the board before demo day. They're most likely to end up pivoting to well-known problems, therefore the clustering around a few common themes. It doesn't explain all of the data, but it's a big part of it. When you have to come up with a fundable new idea in a week and prove it out in a month this can happen...