The mach-o format supports a “fat binary” that contains multiple architectures and then the App Store can only deliver one of those architectures to a particula

The mach-o format supports a “fat binary” that contains multiple architectures and then the App Store can only deliver one of those architectures to a particular device. Bitcode lets Apple recompile a different architecture slice using this format. However, since this change is unrelated to the architecture it can’t take advantage of this format.