All the original compilers like Lisp and Fortran were written in assembler. But that doesn't mean it was easy, or that the resulting language was very capable by modern standards. The thing about Forth is that it is easy, and you get a full-featured Forth when you're done.

That's not to say it can't be done in Lisp but Lisp needs a lot more runtime support than Forth. If I was going to bootstrap a Lisp, I'd bootstrap a Forth first and then write the garbage collector for Lisp in Forth.