Public web archives are a goal, and either we'll deploy a bot to publish them, or I've heard rumors this feature may be added to Zulip itself.
In the meantime, it's kind of nice not having everything immediately publicized. We've had (knock on wood) exactly zero problems with spam users, even though it's open to everybody with a Github account. I'm also (if temporarily) enjoying the freedom to talk a bit more intimately, for example I'm discussing a major project I'm considering taking on.