While that's generally true, chat is pretty straightforward and it's not that hard to set up a IRC or Matrix server and direct users to download and configure a client. Besides, when Slack goes down all the time, your IT guys are going to have to deal with users complaining anyway.
> your IT guys are going to have to deal with users complaining anyway
Except that IT can say "Complain to Slack or complain to your manager that we shouldn't use Slack. Don't complain to us."
This is remarkably valuable--doubly so if your management is stupid and regards IT as a cost center instead of as something useful.
> chat is pretty straightforward and it's not that hard to set up a IRC or Matrix server and direct users to download and configure a client.
Is that true? Take Single-Sign On, for example. That's remarkably non-trivial for IRC. I'm skeptical it's any easier for Matrix/Slack/etc.
If I own this service, it's not enough that I just reboot the service when it goes down. I'm now responsible for when it's slow, when it doesn't do what someone expects, when the user doesn't understand what the service does correctly, when someone forgets their password, etc.
"Foo as a Service" is as much (or more) about transferring the customer service responsibilities for dealing with the end users as it is for delivering the service itself.