I could explain it as Dart not having any features other than what any of the mainstream language has but that would not be much of an explanation would it? What is special about Dart?

I'm aware we have plenty of mediocre mainstream languages existing right now, but they all exist for historical reason and have rather useful ecosystems. However, to go out of the way to just make a new lame ass syntax, with zero ecosystem, and no distinguishable characteristic (which is why Flutter is always involved in selling it) why would you do that?

I'm all for new new paradigms, languages that are different like haskell or scala to flourish and teach us new ways of thinking, this is not it.