The first thing I thought of when I read about Yahoo enabling this was how bad they have been with security in the past and wondered who might trust Yahoo to provide a service like this. Who doesn't remember the huge hack they had a few years back?

https://www.npr.org/sections/thetwo-way/2017/10/03/555016024/every-yahoo-account-that-existed-in-mid-2013-was-likely-hacked