People I’ve worked with have had that idea, and I’ve found they’re most frequently from the games industry or from contract shops. In both of those, the maintenance of the code over time is far less important than that it works on the ship date.

Additionally, people with large state machines with too-complex sets of possible states (games, big frontends without a top level state management system) tend to only unit test because it’s frequently too much of a pain to set up an integration runtime environment. Places with lots and lots of manual QA testers.