There were a lot of factors that led to the dart decision. It's also important to note that Flutter is very old, we were designing it in 2014.

- we wanted hot reload

- it was supposed to feel familiar to web developers and reasonable to native developers

- iOS needed AOT compilation for speed since we couldn't use a JIT

- TypeScript had literally just reached 1.0

- Swift looked promising, but the Oracle lawsuit made the idea of using it tenuous

- Kotlin was not even 1.0 yet, that wouldn't happen for 2 more years

- Go made huge binaries. The language was also lacking features like generics and Go was unwilling to add them (remember this is 2014).

- v8 was not interested in AOT, but Dart was willing to dramatically invest in flutter

There were probably other reasons too I'm forgetting.

Dart was a really pragmatic choice to ship quickly. I have mixed feels about how the decision has aged over time, and wish we had things like Hermes and WASM back then, and a willingness to build a TypeScript compiler like other native frameworks (ex. Valdi)... But for the time I think the choice was reasonable.