One big source of both delays and bugs is the feeling that your work (which has compatibility impacting changes) _has_ to make it in the current release, because otherwise it will languish for years until the next train leaves.
Likewise, if a fix requires a behavioral change that impacts third party developers, that fix may not feasible to deploy until the next release. Apple had some pretty fundamental things like Cocoa outline views broken for multiple years because the fix required API changes.
Understandable from a developers perspective but this is what management is for. This is a great indicator that Apple's current software management is doing a bad job. Because their job is to say no and come up with the plan that will make the software quality and one time. It's really the only thing they do that matters
Likewise, if a fix requires a behavioral change that impacts third party developers, that fix may not feasible to deploy until the next release. Apple had some pretty fundamental things like Cocoa outline views broken for multiple years because the fix required API changes.