I've noticed a lot of business/corporate people really don't "get" slack the same way an older person is bewildered by something like snapchat. We have a "legacy" (for lack of a better term) Lync system that they are holed up in and the split along those lines is very noticeable. Those same type of people who are on the teams firmly on the slack side tend to stay offline until they get an email notification, answer the mention or DM and then disappear again.