In our early days of Zulip-use, I had to regularly edit people's messages to force them into using a topic. A handful of people still don't get it and treat topics as special/long-lived channels, but most of us devs love it.
You can break messages off into other topics, and we have one long-lived channel per stream, which I've found helps (you don't always want to make a new thread to post a one-off link).