Because I would really like to know if I'm affected. According to "Have I Been Pwned" my phone number is not in the list, but about one or two weeks ago I noticed that my spam folder was unusually full, which led me to believe that something new must have happened. Shortly thereafter Facebook's leak hit the news.

From my point of view it is their obligation to notify all the affected users. It's morally the right thing to do, and legally, well, I don't know, but maybe the GDPR says that yes, that it's their obligation to do so.

And with notification I mean to send a notification email, since I haven't logged in for months and don't intend to this year.