That would kill a lot of old software, though. Especially games.
I challenge you to find old software that still runs on modern Macs which was never code signed. Note that support for 32-bit applications has been retired, and x86 applications will eventually be sunsetted as well. This isn't Windows.
Indeed, the current state of affairs on the Mac is the consequence of Apple repeatedly making this kind of choice. That doesn't make it any less frustrating when things that worked before, stop working after.
I can run any open-source software I want. Other people can't run my precompiled binaries unless I opt into an attestation system that lets the OS respond to and pre-emptively block binaries from developers found to be issuing malware. Open source is unaffected.
I seriously fail to see what is wrong here.