How could it not be ?
Yahoo's handling of flickr push user away for years.
do you remember the password of that email account you have not used for 5 years ? good not try to log in and discover that this address has been deleted or reclaimed by hotmail for being inactive.
Do you still have the phone number you had in 2005 ? chances are you have changed several times.
I don't even know most of my current passwords, I never give my phone number for privacy reason (still have about 2-3 telemarketers calls a day for having given it a few times in the past) and I usually can't check the associated email because I don't even remember which temporary email address service I used to register with your service to protect myself from the spam and reselling of my address.
I've learned a lot since the 90's and I trust the web services for exploiting, reselling any piece of info I may give them so everything is single use or fake, it has proven very effective at keeping annoyances at a very low level.
Funny that you would mention a potential security issue when yahoo's credentials and user data has been breached, twice.