Even in a relatively open organization where conversations and work are public/discoverable by default, there's still a huuuge difference between the level of curiosity required to join a convo happening in the office kitchen while you're waiting for a coffee to brew vs needing to spend your idle time at work discovering places (Slack channels or whatever else) to chime in while hoping you're not a distraction for others.

I'm a pretty staunch defender of remote work for most roles, but outside of the smallest companies where the entire organization is on a single conversational thread, you really do lose the organic peripheral vision that comes with an office environment and deliberate effort is required to try and recreate some of that in your fully-remote org if you want some of the same upside. Even with deliberate effort, I'm not convinced you can match it perfectly.