This was not a design consideration when usenet was being developed, because the assumption was all the users would have a name, email, and traceable identity so if you acted like a stupid shit, everyone already knew exactly who you were, where you worked/went to school, and could apply actual real-world social pressure to you to stop being a stupid fuck.

The first email spammer got a call from the US Air Force Major in charge of ARPANET and nobody send spam for a while. We should have kept doing that.

The image is a cropped xkcd with the text replaced but the same joke.