AMP is just a fork of HTML, creating more pressure and work for publishers to implement.
The reason why they do it is because of better search page placement in Google. It's unfair and wasteful, since site speed can easily be measured by the most advanced search engine that already has tools and reports doing exactly that.
AMP is not a search ranking signal. Non-AMP pages will end up in the carousel in 2019... if sites can easily be sped up, why do 80% of websites still suck so much and are slow? AMP won't be for specialized dev teams, but it helps plenty of average websites.
The reason why they do it is because of better search page placement in Google. It's unfair and wasteful, since site speed can easily be measured by the most advanced search engine that already has tools and reports doing exactly that.