…d to take into account when building, marketing and selling a social tool like Slack is psychology. You will become successful if people feel emotionally locked in because of social pressure. And this pressure makes them invest heavily in your product. (Slack actually needs people to invest a mere 2000 message for the effect to take off)
The reason is that they all either implemented threaded comments or didn’t put a message limit. The result is that you don’t have to check the conversation all the time, because you can always take part in it later. Even years later. There’s no social isolation effect, no addiction effect and no reason to keep checking.