- The ops team are in a different country, and are wedded to very old-fashioned views of administration ("Automation? But I like manually running commands from a runbook!")
- You work with a team of people who are quants/actuaries/scientists/engineers but not professional developers, but you want them to have a turn-key environment so they can Get On With It. When they need new python packages or god forbid upgrade pandas or something else, there's a full CI chain that'll make sure that what they do here also works there.
- Swarm is (from personal experience) easy enough to teach people who don't know anything about Docker. You can show them how to query the state, modify it, look at logs, etc. all without the hassle and overhead of configuring and running K8s, even though it will always be my #1 choice for tech-literate orgs. Swarm, for many, including myself, was a pragmatic choice -- 80% of the immediate benefit of container orchestration with 20% of the cognitive overhead for the chaps in another country who had to maintain it if things went south.