I wasn’t a party to that decision, but I think it’s a good one. In my opinion:

• it’s much better for the community: no passwords are stored on the community server, and thus it’s not the community’s responsibility to ensure better server security; and, if there is a breach, it will be on the google/etc end, where their huge paid teams of security experts will be all over it, rather than requiring the volunteer admins of this community to become security experts.
• it’s better for the user: as a user, I have more trust in the ability of the google team to proactively prevent security issues than I do with the volunteers here (no offense to Don and the others). And, as a user, I find it easier to be always logged into Google, and just have to every once in a while (once a week) have the community ping google’s OATH server to verify I’m still me. (it also means fewer passwords to remember).