Jack, no people are doing that - the system won't permit it. The system, however, flouts its own rules. This happens when you add a sibling to a profile that does not have either a father or mother. The system automatically creates a father, using Unknown for first name and the LNAB of the profile you are adding the sibling to. The system adds no other information to this profile - not even the required Biography and Sources headings - and it doesn't tell you that it's doing this but you are now the profile manager of it.
I have, on several occasions, been accused by data doctors of having wrongly removed the headings and <references /> statement on such profiles when I didn't even know they existed.