How do you know who has been in these breaches? Are websites like haveibeenpwned doing business with hackers to get a hold of emails and websites? And just beca

How do you know who has been in these breaches? Are websites like haveibeenpwned doing business with hackers to get a hold of emails and websites? And just because one person discovers an open server does that mean that hackers have also discovered and copied all the data? I'm just confused about the actual technical aspects about data breaches.