In reply to Sam.

AMP has been a testing ground for new technologies to improve the page experience. Several of them are on the road to becoming standardized outside of AMP. See Standardizing lessons learned from AMP.

Also, AMP is no longer a Google project. It is under the OpenJS foundation, same as jQuery and Node.js. AMP has an open governance model. It's not just for the benefit of visitors to Google search. Twitter also links to AMP pages. Microsoft has also linked to AMP pages in Bing.

That being said, it's true that you do not need AMP to make a fast website. Google even has made this explicit this year with the announcement of Core Web Vitals. Any page that has the similar performance as AMP pages can receive the same treatment in Google search. (For example, Top Stories carousel on search no longer requires AMP.)

In the same way that WordPress democratizes publishing, AMP's goal is to democratize performance. While you can make a fast website from scratch, it is very hard to do so. In WordPress this is particularly so given the huge variance in quality among themes and plugins. The AMP plugin is an enforcer: it provides performance constraints to help ensure that visitors will be able to get a good page experience.