Because it does not have a objective scoring criterion.
As phrased the shown challenge has a single correct answer. We require challenges with multiple correct answers which can be ranked, so that you are encouraged to improve on your answer.
As such this is either regular Q&A and as it says in our tour page:
We are not a Q&A site.
Or more likely it's a puzzle. It's not a programming puzzle, which is a jargon term here, but it's a puzzle about programming. If it's a puzzle you will probably actually have better luck on the puzzling stack-exchange, where I believe it would be on topic. But of course you should check their rules first.
Lastly I should mention that the sole exception to this rule is tips. Which is a form of Q&A which we occasionally do. But this is not tips it's a different thing.