[alwillis]

> But aren't they able to do incremental builds and separated x64/arm64?

During the PowerPC to Intel transition, they did stuff like that; perhaps at their current scale, there's reasons why they don't.

Supporting both architectures enables a macOS install to boot an Intel Mac or an Apple Silicon Mac, which is useful in a dual-architecture environment.

It's easy to check for dual architecture support; just use the file command:

    $ file /bin/ls
    /bin/ls: Mach-O universal binary with 2 architectures: [x86_64:Mach-O 64-bit executable x86_64] [arm64e:Mach-O 64-bit executable arm64e]
    /bin/ls (for architecture x86_64): Mach-O 64-bit executable x86_64
    /bin/ls (for architecture arm64e): Mach-O 64-bit executable arm64e