You realize that this one example actually proves the rule, no? In order for the math to work out in this instance you need a large, tech-focused community that

You realize that this one example actually proves the rule, no? In order for the math to work out in this instance you need a large, tech-focused community that might one day turn into a workforce of engineers that might then bring their Slack preference into new companies. At which point assuming the company isn't already using Slack, which is a very big IFF, you then hope that the coder builds enough clout in the company to evangelize Slack and convince the company to move off of whatever they are currently using. If I were Slack I would generate migration assistants to get organizations like this OFF of Slack and on to something like Gitter ASAP. Seems like the return on that investment (in purely good will) would be much more predictable and scalable.