I think you’re misunderstanding what happened in this situation. Nothing was stolen from 23andMe and no 23andMe accounts were “hacked into”. The “hack” happened on another site and the hacker got a database leak of usernames and passwords for that site (not 23andMe). Some of the users of that site used the exact same email addresses and passwords for their 23andMe accounts.

If you use “Hunter2” as a password for all of your accounts and AOL gets hacked, the hackers know your password is “Hunter2”. If they get into your Facebook or Gmail account because you also used “Hunter2” there, that is neither Facebook’s or Gmail’s fault. It is your own fault.