Because the breach wasn’t on 23andMe. It was on another site.
The only way you’d be affected by this is if you used the same password on multiple sites (where one of those sites actually had a breach) or if you shared your DNA profile (since it is opt-in) with someone that reused passwords. In the latter case, only the info you shared with that person would be accessible to someone using a compromised account.
In other words, if you shared your info with someone you didn’t know and didn’t trust, your info can be used by bad actors.
The only way you’d be affected by this is if you used the same password on multiple sites (where one of those sites actually had a breach) or if you shared your DNA profile (since it is opt-in) with someone that reused passwords. In the latter case, only the info you shared with that person would be accessible to someone using a compromised account.
In other words, if you shared your info with someone you didn’t know and didn’t trust, your info can be used by bad actors.