Google can't "simply preload resources of non-AMP pages". Using a CDN means they can get more consistent load times and avoid the inevitable privacy concerns that come with loading 3rd party content the user may never actually click on.

Being forced to load everything you read via Google is worse for privacy. There are already plenty of solutions for blocking 3rd party scripts, like Privacy Badger and umatrix.

Google already has your IP; it's their page. Preloading resources from it's own CDN doesn't tell them anything they don't already know. Preloading resources from someone else's domain would.

They could CDN people's non-AMP static content for this purpose though. It's not like their search engine isn't caching a lot of it already anyways.

Just how do you imagine they'd "CDN people's non-AMP content"? There's no mechanism by which they could tell the browser to load nytimes.com but to replace the URLs of random resources with different ones.

They'd need to host the actual page on Google.com. And after solving all the problems that doing this introduces, you've pretty much got AMP already.

Even if you can't package up and ship all of your traditional site to Google's CDN, you could do most of the burdensome/heavy bits. But then Google doesn't get to control your website and define the way it's allowed to look, which is what AMP is really for.