"how is insider trading tracked?", was recently migrated to money.SE.
I migrated that question along with this one from the same user. When the answer to his question is simply "Form 4" or "short interest", then it doesn't belong on a quant site. For that matter, those questions would be pretty basic for any site dedicated to professional trading, quant or otherwise.
Although it is not universally true, generally questions that are finance related but have no quantitative content (such as the question you reference) would be more appropriate to the Personal Finance & Money site. However, some questions that would be inappropriate on any stack exchange site should be closed here rather than migrated.
As to why was it migrated now, you'll have to ask Chris, but I suspect it was just some overdue clean-up.