where is PHP getting more traction than Perl from?

mod_php is more useful for bulk hosting than mod_perl because mod_php is less powerful. As a system admin, you don't want a user you don't personally know to write a handler, or to be able to do internal Apache things (like play with subrequests and internal redirects). And even though having an eternal interpreter and an API to communicate directly with Apache make mod_perl so fast, not having an eternal interpreter is what makes PHP much easier to work with and much more reliable in case of sloppy programming, and not having that API would comfort sysadmins more. Perl interpreters are very heavy, and that would need to change before a mod_php-ish thing can be made with Perl. The closest thing you can get now is letting the process that handles the request die. You then skip startup overhead by CoW forking, but don't have the risks involved with having your interpreter live on.

Summarized: mod_perl is too powerful to compete with mod_php on the bulk hosting / idiot programmer market, and unfortunately, that's where popularity lies.