Ultimately there is only one reason that matters: The person in charge of deciding what communication channel to use likes Slack/Teams/IRC/whatever.
Add to that the SaaS propaganda that hosting literally anything yourself is just too hard (it really isn't).
Or this notion people are just too stupid to deal with anything more than the simplest possible web interface - Really? what do those people even do? Stare at Notepad all day? Of course not. They stare at various complicated software packages ranging from CAD, $spreadsheet abominations, SAP to various Adobe software packages.
Sprinkle in a bit of hype for the latest new thing and presto..
</rant>
Add to that the SaaS propaganda that hosting literally anything yourself is just too hard (it really isn't). Or this notion people are just too stupid to deal with anything more than the simplest possible web interface - Really? what do those people even do? Stare at Notepad all day? Of course not. They stare at various complicated software packages ranging from CAD, $spreadsheet abominations, SAP to various Adobe software packages. Sprinkle in a bit of hype for the latest new thing and presto.. </rant>