OAuth 2.0 took the best features of what was already being deployed by Google, Microsoft, Yahoo, etc. and added in scopes and refresh tokens. The objective was to standardize how to delegate authorization so that developers did not have to learn slightly different ways of doing effectively the same thing.
Typing your username and password into a 3P website so it could crawl your contacts was horrible anti-pattern.
Typing your username and password into a 3P website so it could crawl your contacts was horrible anti-pattern.