1. It would be impossible for the user to voluntarily give up rights to information they may not understand.
2. It would be impossible for the app to act on behalf of a user.
3. True early adopters are not deterred by the lack of quick sign-in if they truly love the product.
4. Signing up with email is easy today, and browsers make logging in an automatic and smooth process.
5. Emails already act as zero-permission identities.
Furthermore, I don't have to worry about having a user account system that has to be ready to deal with N different OAuth tokens. Personally, I have found OAuth to be a very inelegant technology.
Next time I build a website that has accounts, I will try and market the lack of "signing in with Facebook" as a boon to the user. OAuth is a slippery tool for collusion, something I never want my customers to be victims of. I cannot advocate for technology that is primarily used to extract information from passive people.
Making the rules so hard to read that the average person just says "yes" was unethical in 1492, and it's unethical now.