It’s only maybe for the past two years now that it’s even been promoted as a general purpose language, which I think was a huge oversight on the Dart team’s behalf. For a long time they would just promote it as a great way to build UIs. What ever drove them to talk about it like that originally is beyond me.
The competition is too strong. At a team or organization level, where neither uses Flutter, why would you use Dart when C# and Kotlin exist? Both have better performance, better UX for doing common application tasks and vastly bigger ecosystems.