I seriously can't overstate how easy it is to sign a binary. You don't need an Apple Developer account, or an internet connection, or anything other than macOS and a working development environment. Just go into the Terminal and type:

> codesign -f -s - [path to binary]

Unless something has changed on Apple Silicon, that's it, you're done, the binary has a signature. It does not have a trusted signature, but you don't need one. I think it was just simpler to write the OS assuming all executables would have a signature.