Probably because the part most of the world is actually interested in was later renamed 'Open ID Connect' and any attempt to research using the term OAuth will bring you nothing but incorrect, old, ad-hoc implementations and presentations by snake oil selling 'personalities' claiming they understand it.
And once you realize you actually want OpenID Connect and none of the OAuth 2.0 features, you stumble about the fact that OpenID is not what you want because they just share a name... Where was I again ???
Naw, the same applies to oidc. Especially in the browser.
The issue itself also sounds easy enough to implement that you might get suckered into rolling your own (you only need to do a redirect and a request every n-minutes) ... But it's surprisingly hard as there are a lot of edge cases with long running timers and potentially multiple browser tabs/windows etc.
