I did not question whether Steem auth should be preferred or not but that it is not included among others means to log in. But I can understand it as Steem does not hold any personal data and thus making it significantly different than signing in with other accounts.
I agree that the decision is good for people who don't know Steem and may decide later whether they want to join. Though, if Steem is not required and people may use the platform without a Steem account, they may miss the potential of the blockchain and may not join other apps. But those thoughts are out of Utopian scope.