A human is behind an account. There need to be ways to recover an account when certain measures fail with non-tech savvy folk like my elderly parents. Yahoo offered no way to recover the account.
I know a bank that purposely reduce their Internet banking security. To cater for specific elderly customers who constantly forget their password. They are not going to force their customers to walk into the bank everytime.
These accounts are at a risk of getting hacked. It's called a tradeoff. As a bank, do you want customers or not? Do you like money or not?
As for the Yahoo situation. If they gave a shit about customer service: they can accept copies of drivers licence/passport signed off by a justice of peace.