What prevents an EC2 instance from going down in exactly the same way? Other hosting providers offer automatic backup too - it's not an AWS exclusive feature.
So if you app enters a crash-loop and fails to start an AWS engineer comes in and fixes it? Because that has not been my experience..
The truth is that there's still a lot of things you have to handle, including cloud bugs and problems. And other problems you don't have to think about anymore, especially with fully managed, high-level PaaS- like services.
I ran a cloud backend service for a startup with users, using manged services, and we still had an on-call team. The cloud is not magic.