I did not work for Apple but this article describes exactly what I was thinking. Apple has very waterfall cycle. Everything is planned year after year to be released for the September event. When the deadline approach teams realized that are behind and they need to overwork. And when people get tired and under pressure, they usually introduce even more bugs. The article also nails the solution: a more Agile workflow.…
The real problem is that Apple needs to loosen the secrecy between engineering teams, as there's no good way to tell if your new Safari feature breaks something in System Preferences because the System Preferences developers are in another building and aren't under the right NDA to learn about your new Safari feature.