That is because there is literally no secret in large volume purchase and production in Supply Chain. You are talking about a product that will be sold in 100+ millions in following 12 months. Apple used to keep secrets very well because they were tiny. And there were way less Apple fans then. Now reporting news on Apple has become a big business in itself, so much Bloomberg decided they need a whole team just to report on technology and Apple related news. Apple Keynote was watched by 20M people in 2014, I wouldn't be surprise if the number are now over 50M, that rivals many of the most popular sport's top league live viewers.

But when the product is totally not in the radar of journalist, they came out of no where. AirPod for example, is one of best Apple innovation in recent years. It was simple, and it works. Try getting any older bluetooth Ear pieces works and I would throw them out of the windows within 5 min. it worked so well that everyone is using it, and they were selling like hotcakes. Since AirPod is now on radar, there is no escape in media trying to poke at people and supply chain.

Having said that, they could have done a much better job in software secrecy, since they control everything within it. And yet time and time again Apple seems to not put much care into protecting its secrecy.