Wolfram hates Lisp, he believes Lisp is too slow and not C/C++ enough for his liking.
http://coding.derkeiler.com/Archive/Lisp/comp.lang.lisp/2004-06/1236.html
Wolfram wrote SMP because he felt that Macsyma, which he used
extensively, was too slow. Wolfram thought that he was
cleverer than anyone else and could read Knuth's books and
then write a better computer algebra system. He wrote it
with
S. Cole, Geoffrey C. Fox, Jeffrey M. Greif, Eric D. Mjolsness, Larry J.
Romans, Timothy Shaw, and Anthony E. Terrano.