I helped a Slack competitor with sales for one job. They said they avoided marketing to tech companies because it's really hard to convince techies that Slack is better than X, and many were fanatically attached to it.
However, they have a very good market share with non-tech companies - food industry, construction, hospitals, etc.
It wasn't so much that it was a bad app for tech industry, more that it's hard to penetrate the market. The other industries were dealing with WhatsApp groups and needed something better, and even considering building a solution themselves.