I suspect the availability of yacc/flex/bison and the free (as in freedom) Gnu Compiler Collection are also a pretty big influence. They give a (monetary) low

I suspect the availability of yacc/flex/bison and the free (as in freedom) Gnu Compiler Collection are also a pretty big influence. They give a (monetary) low cost of entry and a substantial amount of utility - I suspect a language inventor would prefer to invent the language and have the lexing, parsing, and code generation already taken care of by someone else.