While the six subjective guidelines cover the question...in question, the closure is actually due to the next part of the close reason:
All questions should be practical, answerable, and of some educational value to the greater community. Chatty, open-ended discussion questions diminish the usefulness of our site and push other questions off the front page.
The question has 53 had answers, which is a good sign that it's open-ended and unanswerable in its current form.
Answerable questions—even subjective ones—should be getting 5 or 6 good answers: that signifies the question was a specific enough scope that there were only so many ways it could be answered correctly.
When you start getting into 20, or 30, or worse yet 50 answers, it's highly unlikely the question was of a specific enough scope for anyone to learn anything from the answers. Nobody's going to read and test 50+ answers to see which one works for them: it's unreasonable. So instead, what you're left with isn't a Q&A pair that solves a problem, but a discussion or a poll of people's opinions about a topic.
More info about this, including Jeff's answer from around the same time the question was closed, is found at:
Too many answers is the sign of a bad question