How does that level of transparency for a public company not lead to insider trading?
Usually only executive-level and higher employees have access to information considered material to the business trajectory at large. Emphasis on usually; all that boring bigcorp training covers the ins and outs.
But when you have access to info that could conceivably impact the stock price if revealed, you cannot do any trading even during those trading windows. That's why the top execs can typically (always, I think) only trade via pre-planned schedules.
I've been placed on the insider list in public companies when involved in secret projects (future acquisitions, typically) and that means zero trading for the duration of the project regardless of when employee trading windows open or close.