Zulip founder here; I'm curious why you think that?
Here's our thinking. Topics within a stream are ordered by the time of the most recent message. We keep the complete history, both of messages and topics, because it's useful for search and following up on things. Personally, I regularly reply to a conversation whose last message was a month or more ago to follow up with new information (often after getting there from one of the permanent links in our issue tracker). Because the context is all there and available with just a single click on the topic, I find it to be a really nice workflow.
Here's our thinking. Topics within a stream are ordered by the time of the most recent message. We keep the complete history, both of messages and topics, because it's useful for search and following up on things. Personally, I regularly reply to a conversation whose last message was a month or more ago to follow up with new information (often after getting there from one of the permanent links in our issue tracker). Because the context is all there and available with just a single click on the topic, I find it to be a really nice workflow.