It's based on Dart, a language that already failed to take off in browsers? Just a guess.

I think it's more of an issue with it coming from and being maintained by Google. I think aversion to Dart is overrated; it's a boringly stable and straightforward language, and I'm puzzled that mobile developers aren't more open to learning it, given how Objective-C/Swift/Kotlin were languages that most had to learn for developing on their respective smartphone.