The easy answer is that AMP forces you to do things like always declaring image height and width. And yes I could do that without AMP, but the moment you're not

The easy answer is that AMP forces you to do things like always declaring image height and width. And yes I could do that without AMP, but the moment you're not forced to do something, the path of least resistance is to not bother. I certainly never would never have bothered setting up a build process to inline CSS previously.