Perl is the de facto standard for CGI programming for a number of reasons, but perhaps the most important are:
The advantage of an interpreted language in CGI applications is its simplicity in development, debugging, and revision. By removing the compilation step, you and I can move more quickly from task to task, without the frustration that can sometimes arise from debugging compiled programs. Of course, not any interpreted language will do. Perl has the distinct advantage of having an extremely rich and capable functionality.
There are some times when a mature CGI application should be ported to C or another compiled language. These are the Web applications where speed is important. If you expect to have a very active site, you probably want to move to a compiled language because they run faster.