[Barrin92]

convenience is the obvious one, normal people don't enjoy handling 50 different accounts. The less obvious but arguably more important one is safety. In ye olde days and still today random sites generally don't really know what they're doing and with OAuth you're not leaking your data to some server in a basement that get's pwned every few weeks. If you use Google or an equivalent service to login you retain control over your credentials.

[syslog]

And then Google decides for no discernable reason to lock your account, making it impossible to login _anywhere_.

I get the convenience and also the security benefits, but there‘s a whole lot of risk, too.