Hell, Yahoo had entire verticals like ocean shipping self organizing around Yahoo Chat back in the day and never figured out how to monetize. Slack is going to be another salesforce widget.
And they're both monetized exactly the same way, as part of a more comprehensive suite of office productivity offerings. People don't pay for Yahoo Chat the exact same way they don't pay for Yahoo Mail.
Chat is almost always a closed loop. There are usually large implementations, and as a user I can only message within one. There are some exceptions to that. Chat always gets kicked around as corporate strategy changes. At work, I’ve probably used a dozen incompatible Microsoft solutions as their strategy meandered around. Jabber was the big attempt to make chat like email, and it failed.
Email still runs the world, despite its many flaws.
...this would make the problem you identify worse. Signal is one company.
> E-Mail is an open Standard. Instant messaging can be too!
It can be, but Signal definitely isn't.
Email and instant messaging don't actually differ in terms of what they're doing. They differ only in the social perception of what you should use them for. Why not use, say, Delta Chat, which is a messaging app frontend that delivers its messages by email?