The original mission of replacing JS in the browser failed. At that point they could've called it off. Instead they doubled down with Dart 2.0, which, could've been great if there is actually anything 2.0 about it. It's still just some language with curly braces.

During the same time frame of Dart's existence, other languages that actually have innovative ideas were able to carve out their niches (go, rust, ts, kotlin, swift... list goes on), while Dart still has to rely on some UI toolkit to sell.