I think it was a way for Google to get newspapers and other publishers to stop smothering themselves in ads. Google has been preaching the gospel of the fast web for years now as publishers add yet another box for an ad server to fill.

Then Facebook started to court publishers and suddenly the best way to read a lot of web content was inside of Facebook which is obviously terrible for Google. So Google came up with Amp as a way for publishers to provide the same experience on the web.