What I think is difficult is that most people think a website should be an experience.

The client wants this, the designer wants this, the marketeer wants this and even most users want this.

So that's how huge headers with high res photo's are born.

After that the site must be online asap and the developer doesn't have or take the time to load images responsive.

Combine this with a framework that takes 200ms to init and we are where we are now.

(And then ofcourse there is the marketeer telling you to include a script from x,y and z.)

With the right tools you can build a fast web, but I think most developers are not experienced, lazy or just don't care. (You don't need to include 0.5MB of FontAwesome when you only use 2 icons...)

And yeah: AMP is a joke.