[pjmlp]

A programming language is more than just semantics, Dart eco-system is a tiny dot when compared against C++ and C#.

Flutter deployment times aren't worthwhile enough to bother with a language with uncertain future.

[Apocryphon]

Doesn't Dart interop with JavaScript libraries?

[pjmlp]

It does, given its history.

However that is very little against C# and C++, which can also be compiled to JavaScript/WebAssembly.

Additionally there are TypeScript, ReasonML, and a myriad of other languages with JavaScript interop.