https://www.google.com/amp/s/amp.reddit.com/r/explainlikeimf...
Basically it's a way for google to promote web pages that are better formatted for mobile devices that use a limited subset of html and restrict use of javascript. The pages are hosted on google.com as additional assurance that they will load quickly.
I do believe it's scary to some because it seems like it's giving google a lot of power and control over content on the web.