Slow sites are more than just HTML overload. Slow sites typically have additional HTTP requests (loading external CSS/JS files, AMP doesn't allow JS or external CSS files). They also load all images at once (AMP does lazy content loading). They don't cache as well as AMP does.
For companies, it's a framework that restricts the "bad" requirements that conflict with page loading performance.
Async just tries to load everything at once. If you're on mobile, you could have a slow connection. Trying to load an image at the bottom of the page at the same time as an image at the top of the page would compete for bandwidth. The idea behind lazy loading is that you give top priority to what needs to be downloaded right now.
You also don't bother loading what will never be seen, assuming the customer doesn't scroll down to the bottom of the site. This improves the customer's battery life because an HTTP request uses the radio which taxes the battery.
Further, by abiding by a set of standards, Google and others can trust the content will load quickly. That trust allows them to feature the content higher up in search results.
> Further, by abiding by a set of standards, Google and others can trust the content will load quickly. That trust allows them to feature the content higher up in search results.
So it is a Google closed club? "you use our library, your site ranks up"? I doubt this is true. If it is, I doubt it will endure. If it endures, I doubt I wish to live in this world.
> So it is a Google closed club? "you use our library, your site ranks up"?
Yes, unfortunately that is exactly the case.
Try a Google search for any news-related topic on a mobile device (at least in the US) and you'll see that only Google AMP pages are featured in the top scrollable news widget:
That's why most of the major publishers are providing AMP versions of their content. You can find the linked AMP version of any news article by checking the HTML source and looking for the "amp" link tag in the header.
For companies, it's a framework that restricts the "bad" requirements that conflict with page loading performance.