The problem with mod_perl for hosting companies was that it was much harder to protect global variables from being visible from other accounts on the same machi

The problem with mod_perl for hosting companies was that it was much harder to protect global variables from being visible from other accounts on the same machine. It also consumed a lot more memory than mod_php from what I remember so it never became a part of the shared hosting scene which enabled PHP to flourish. Mod_perl was also a lot more complicated than CGI Perl which is why Perl remained only a CGI option on cheap hosts. Some very big sites ran on mod_perl but they were running on dedicated hosts, not shared.