Slack is free for small teams that don't need lots of chat history. By the time you get big enough to need those features, you probably have some standard platform in place for email, almost all of which also have chat solutions from the same vendor.
So I'm not terribly interested in new competitors in this space because for larger orgs, chat is an add-on to other services, and I don't want to bring in a new vendor just for a chat alternative, even if the existing solution has problems.
Basically, price isn't the true barrier - simplicity in vendor relations and enterprise tech footprint is the bigger concern.
