Why is it necessary to prevent direct access to included files? For example:

    if ( ! defined( 'ABSPATH' ) ) {
        exit; // Exit if accessed directly.
    }

I notice many plugins do this but I don't see it in WordPress core files (such as [capabilities.php][1] for example).


  [1]: https://github.com/WordPress/WordPress/blob/master/wp-includes/capabilities.php