I can't speak to why the other users voted to close your question, but I would have closed it myself and here's why:
First of all, it's more of an art contest than a programming contest. Challenges like that aren't on topic here since the site is about programming.
Popularity contests, i.e. challenges which are scored by the number of votes, are difficult to do well. In particular, they need very specific guidelines on what is expected for the task and what makes an entry deserving of votes. In this case, the only rule is "output random characters and say 'matrix effect'."
Even if this were well specified, it would be hard to make it sufficiently distinct from Make the Matrix Digital Rain using the shortest amount of code.
I encourage you to post your challenge to the Sandbox for Proposed Challenges where you can get meaningful feedback from the community before the challenge is posted to the main site.