You don't backport - you create a separate hacky patch for the older codebase that temporarily fixes the issue. (In fact, that's exactly what everyone does when

You don't backport - you create a separate hacky patch for the older codebase that temporarily fixes the issue. (In fact, that's exactly what everyone does when a serious bug is found in a current version software that they know requires an architectural change for a long term fix). Ensuring compatibility without breaking stuffs (like Windows was once famous for) or long-term support for softwares is not a new concept. What you pointed out in your comments is how Apple prioritises its resource - it's perfectly reasonable to focus only on the latest version of codebase as that is obviously easier, and Apple's business model is built on that. That's the mindset / policy that certainly gives you the luxury to think in terms of changing the architecture to fix a bug the "right" way but at the expense of ignoring older codebases.