ICQ came out in 1996, AIM in 1997, and MSN in 1999. I don't think it's fair to give the people working on this a pass by saying this is a new problem - working products have been shipping for over 20 years. Some of the devs working on Signal and Matrix were probably born after ICQ was released.
The reality is that all of these systems, including email, tend towards becoming walled gardens. Otherwise you end up with the same problem that email has which is that a huge percentage of it is spam. At this point email is basically a few connected walled gardens from the major providers. Before that the amount of spam was even larger.
The problem is not in which year it started but whether the feature set is stable enough to be standardized - see my questions in the original comment. And that's just a few of them.
Each of these chat applications have answered the questions you raised in their own way. Since we haven't converged on a single set of standard behaviours in 20+ years, it probably means there isn't a single right answer.
Part of the problem is that previously they were a value add as part of a service provider. There was no intent to generate revenue from it because the revenue came from the provider's operations. If I'm building a chat client now, though, I've got to find a revenue path. You need the walled garden so that you get lock-in and can find a revenue model from it.
The reality is that all of these systems, including email, tend towards becoming walled gardens. Otherwise you end up with the same problem that email has which is that a huge percentage of it is spam. At this point email is basically a few connected walled gardens from the major providers. Before that the amount of spam was even larger.