- Message history
- Files that have been shared
- Integrations / bots / ...
- Plus you would need to setup everyone again, create channels, ...
Slack goal is to be cheap enough that it does not represent a major cost for the company and integrated enough that moving would be a pain.
The integration story is more interesting, but to _be_ a competitive product many of these must already exist.
The job of competing with Slack is harder than it once was (just look at MS Teams) but not impossible (just look at Slack...) - there’s lots of room for improvement.
I think we moved from Slack to Mattermost because our infosec people weren't happy about Slack's handling of our data; there's a line in an email about "discussions with Slack over the past year regarding their data security and AI initiatives". But then Slack sorted that out to infosec's satisfaction, so we moved back, because running your own Mattermost installation is more of a hassle than paying Slack to do the equivalent.
Microsoft Teams especially seems like a deliberate attempt to dethrone Slack, and while it is slightly more annoying to use, it just makes sense for companies to bundle their services and subsciptions.
I do not really see a bright future for slack.