I mean, it wouldn't but that is the way it works. Ex:

    $ file /usr/bin/ssh
    /usr/bin/ssh: Mach-O universal binary with 2 architectures: [x86_64:Mach-O 64-bit executable x86_64] [arm64e]
    $ file /Applications/Numbers.app/Contents/MacOS/Numbers
    /Applications/Numbers.app/Contents/MacOS/Numbers: Mach-O universal binary with 2 architectures: [x86_64:Mach-O 64-bit executable x86_64] [arm64]

It's probably nice to have a single release for both platforms. And the installer and a clean install is only 12-14GB, not that heavy a lift.