User blog comment:LEGOSuperDKong/New rules for CUUSOO (and the end of many popular projects)/@comment-5955017-20131212220413

The old rules had never quite defined that there could be no 'theme' based projects, though it was suggested that these were frowned on. And indeed, it explains why some of the projects did not pass review.

I can see why they would institute it: when someone makes a theme, it becomes harder to say what profit of it actually goes to the user. Do they get money for books of the series and comics, or just the sets they made or any future sets? This simplifies a lot of the paperwork out.