Same thing that stops it from processing PHP or perl code. If it cannot find a handler for it, then it has no choice but to serve it raw or throw an error.
Check the httpd error logs, they should indicate the problem. Don't know how CF is installed with Apache, but you'll either see errors on startup, on request, or both.
As of PHP 5.5, the MySQL library has been officially deprecated. It is recommended to move to either MySQLi or PDO libraries for your mysql connectivity. See here for help choosing which interface you prefer: http://php.net/manual/en/mysqlinfo.api.choosing.php