I think they are betting on managers and in this regard it's going to work out well for them. After all Slack is a company thing (slowly turning into corporate

I think they are betting on managers and in this regard it's going to work out well for them. After all Slack is a company thing (slowly turning into corporate thing) i.e. the decision to use it will likely be made by those who like WYSIWYG but hate putting stars or backticks in their messages, or don't understand the concept at all. So, in the end it's a very clever move.