The problem is most Wordpress plugins are abandoned. Most sites default to auto updating plugins, but if the plugin author isn’t pushing security patches it’s a big vulnerability.
Wordpress plugins are notoriously bad at input sanitization. Even many large, commercially supported plugins get abandoned or simply aren’t secure.
> Well, Wordpress can know auto-update the plugins...(sic)
And your site (Or some parts of your site) could break at any point in time without your knowledge and remain broken for a long time until you find that it’s broken. There is no platform that doesn’t require “babysitting” with maintenance and testing.
Wordpress plugins are notoriously bad at input sanitization. Even many large, commercially supported plugins get abandoned or simply aren’t secure.