So how do you propose they make money instead?
I'm personally getting a bit sick of it for another pragmatic reason. It's bloody slow to open, slow to switch accounts and even slow to switch channels.
I was able to search years of intensive mailing in both server and local cache in an almost instantaneous fashion in Outlook {2003, 2010 & 2016} for Windows, but Slack can't properly search a year and a half of history without choking. On almost every level, slack is a complete technological failure (where it matters).