They however a few years ago started forcing API users to authenticate, so when I had to spend months in bed after a bad road accident and later a heart attack, I couldn't anymore watch my favorite electronics channels using the Kodi YT extension unless I would authenticate. I guess they still allow anonymous use with a browser only because by doing that they can profile more people.
Furthermore, the economics of video hosting sites like YouTube are such that you have truly incredible storage, server, and bandwidth growth, basically forever. I don’t think it’s feasible for there to be a “free” API that lets people use YouTube as they please, build clones of the site with no ads, etc.
In their client-side code, they provide a worked example of how to use their API. That's hardly the way to keep a secret.