IMO That's opposite of what I understand. The selling point of Oauth2 is SAML works great on web (mobile browsers included) but not so on apps.
The other reason, which I didn’t mention above, but is talked about in the blog post, is we decided to use bitly’s oauth2_proxy as a basis for our solution. This had been widely used in BuzzFeed (we had over 100 auth proxies in place prior to rolling out sso), and so the OAuth flow was something everyone was familiar with.