> More importantly, it was a Google language that they could mold for their own needs, not so possible if it's an outside language like TypeScript. For example, early on, they asked the Dart team to create an AOT compiler since Apple does not allow JITted code apparently (not sure how React Native gets around this then), or maybe it didn't back then, and the Dart team was able to do it successfully for the Flutter team. Try asking the TypeScript team to do the same, it's next to impossible.
Why would you need to modify the language? Dart is the most basic managed language without any novel feature. There is zero reason why, say, java couldn’t have been fitted for this particular niche.
How will you convince the Java team to add things you want to make it work better for your framework? You could try adding them yourself but you'd be forking and making your own Java dialect at that point. They did that instead with Dart which they own.
What would you need for a framework that can’t be implemented as a library? Will we recreate every language from scratch for the next logging, gui lib, web framework as well?
For example, making an AOT compiler. Or adding other features. Or making the implementation more suited to client side apps. There are many things you can do to a language to make it easier for a specific use case. In the extreme, this is what DSLs are.
I don't understand why you don't understand that having first class control over a language's development is a useful thing to have.
Replace TypeScript with Java above.