mod_perl had the issue that it had hooks deep into the webserver, which wasn't "shared hosting safe" mod_php had less hooks and some basic cross-vhost-access mi

mod_perl had the issue that it had hooks deep into the webserver, which wasn't "shared hosting safe" mod_php had less hooks and some basic cross-vhost-access mitigations (Safe_mode oben_basedir etc.) which allowed independent users to put PHP scripts on the same server, which in turn made web hosting cheap.