Re: "73% of users worldwide use their Google or Facebook accounts to log into other apps"
For me, everyone gets a different email address, a different username (if allowed, and unless its a forum like this site, I use the password generator to create the login name too) and a different password. >300 email addresses at last count a few months ago and just checked, 462 entries in my password vault.
Sure, I probably use <10 of them on a weekly basis, but they're all there.
It would be harder to use the same password across various websites. I'd have to dig into a different website's entry in my password vault, note the new site in the entry and hope that the password rules for site I'm copying matches the new site's policies.