Earlier quoted context omitted.
AMP content shows up before other organic search results. So it's not really optional unless you want to lose all your search-driven traffic.
I think Google had to do something, publishers overdid it with their crappy websites with 50 tracking links and banner ads. The mobile web was slowly dying and everything was moving to apps. AMP is their effort to reverse that trend somewhat. I haven't heard any better ideas (Facebook Instant Articles is worse imo).
the main goal of amp is to monopolize it further and make that last one they couldn't buy stop working.