Let's start by acknowledging one external factor that does affect the
popularity of a programming language. To become popular, a programming
language has to be the scripting language of a popular system. Fortran and
Cobol were the scripting languages of early IBM mainframes. C was the
scripting language of Unix, and so, later, was Perl. Tcl is the scripting
language of Tk. Java and Javascript are intended to be the scripting
languages of web browsers.

Lisp is not a massively popular language because it is not the scripting
language of a massively popular system. What popularity it retains dates
back to the 1960s and 1970s, when it was the scripting language of MIT. A
lot of the great programmers of the day were associated with MIT at some
point. And in the early 1970s, before C, MIT's dialect of Lisp, called
MacLisp, was one of the only programming languages a serious hacker would
want to use.

Paul Graham
"Being Popular" - http://www.paulgraham.com/popular.html