Maybe because that's not the only thing it does? It is what Google likes to pretend that AMP is all about, but you're also handing over the control of your traffic directly to Google, and being awarded with the SEO boost.
That's significantly different than debloating your website and remaining in control of the traffic, but you don't receive the SEO boost as a consequence. Even if you make your website faster than it would be if you were using AMP (which is not that difficult to achieve), you're still being punished for not giving control to Google.
