$allowAnonymous = true - not working
It sounds like you just want a cron job to trigger an action on your plugin.

You don't need to register any Control Panel routes for that, so you can remove your registerCpRoutes method.

If your plugin only has one controller, the URL your cron job would want to target would be:

yoursite.com/actions/pluginHandle/pluginAction


You can read more about it in the plugin controller docs.