Comment by kazinator

Extending Lisp can be hard work. Take an existing Common Lisp implementation and give, say, support for continuations.

Adding the necessary syntax will not be hard, however, whereas in a in a different kind of language framework, that part will have difficulties also.

What will also be easier in Lisp is for downstream users to manage the change. For instance, maybe some code relying on the new feature can work fine with some hack that just fakes some the semantics. That can be disguised under compatible syntax.