Well, they are different languages made for different things. Clasp was specifically made because the author had a bunch of C++ code for his research projects, but wanted something more high level/simpler to implement things in. He landed on Common Lisp but none of the implementations had good C++ interop, so he made his own. Can recommend Christian Schafmeister's (creator of clasp) talks on it, it's interesting stuff. In particular his talk on an LLVM Conference.
https://clasp-developers.github.io/clbind-doc.html