I worked on a remote team for several years and recently migrated to an in the office job in a similar line of employment and was surprised how often such things occur. In your case it may either be that your work does not lend itself to such activities or you are potentially unaware that they are occurring.
Slack is poor replacement for face to face. It is good for communication for many types of projects and teams, but it cannot convey a person's facial expressions or emotions that otherwise might be present in their voice. My current organization, while onsite, has teams spread across the globe that we interact with. Attempting to solve complex engineering problems via email and chat is doable, but takes longer than throwing a couple of the engineers in a room with a whiteboard (and so the company pays for travel when that is needed).
In my experience, remote work is very situational. Certain jobs, tasks, and teams will lend themselves to remote work, but those items are not the majority of work yet.