This is what really confuses me about AMP. All it does, really, is force authors to strip their page down to core, performant components.
Another way to do that is to strip your page down to core, performant components without loading a JS library from Google. But Google dangles the carrot of improved SEO with AMP, so everyone has to do it anyway.
(note: they don't actually prioritise AMP pages, they prioritise page load speed. But AMP pages are put inside a Google CDN, so, what do you know, they load fastest)