Yes, all their reasons for not joining a customer slack seem reasonable, but none of them seem related to the 25-year theme. They are all about problems in the here and now, you don't need a quarter-century-long stare to see them.

I felt that it was laid out fairly well in this essay. They described their 25 year rule, and described a lesson they learned in the first 18 months of their company from a few attempts really wasn't working for them. Because they learned this lesson early on they refused a client's request because they were confident in the lesson learned not providing the right kind of value for their organization or their clients. Their rule biases learning from early things that don't work so that they can focus the most energy on things that are working.

Same here. I thought the article was going to talk about vendor lock-in and the inability to access old chat messages if their client removes their access, or if their client stops paying Slack, or if Slack stops existing. The hard turn into that mainstay of startup blog posts - "Slack makes us unproductive" - felt abrupt and unmotivated.

They could see that though they could handle joining a Slack or two now, doing it repeatedly over 25 years would shape the company in a way they didn’t want.