Google can't even serve Youtube using codecs currently supported by its own browser. There is a mode to switch to HTML5 video, but some of the videos require Flash anyway. Besides Google does not indemnify the potential users of VP9 against potential patent infringement, so it's only slightly better than just grabbing an h265 codec and linking against it without first obtaining a license. It's a patent mine field of epic proportions, and if you're going to pay for patents, you might as well get the real deal supported by Microsoft and Apple out of the box, including low-power silicon and GPU support. For Google VP9 makes sense, since they already license MPEG LA IP, so they can both encode and decode with VP9 without attracting legal attention.
Aside from search and ads, Google is all about basically building the fist 80% (sometimes less) of something and then throwing it over the wall to the unwashed masses, or, alternatively, milking the PR in perpetuity. Glass, self-driving car, robots - all PR projects that will not yield a successful product in the foreseeable future. Android and Chrome are basically means of protecting the ad revenue. Youtube's sole purpose is to show you those stupid pre-roll ads. Flash shows them just fine, which is why HTML5 video has been in beta for quite a while now.