Why?
If you’re in the US, you should know this because if you want to apply for a passport, you’ll be required to provide information about your parents such as birth dates and places. If you’re divorced, you will have to provide the same info along with marriage and divorce date, even if it was decades ago. So if you have access to that info, make sure you record it somewhere safe for Future use.
If you’re not in the US, you should know because this information can be difficult for people to get if they never knew one or both parents, or have a bad/non-relationship with them. Or if they had a contentious divorce or an abusive partner. Which is another reason why just leaving the country can be difficult for people who are already marginalized.
Kind of
The vast majority of the time we use our social security numbers as a personal ID number. Drivers licenses also will have unique numbers on them which you can query off of, so too do passports.
By law, no one is required to have any of those three. People having a social security number is pretty common, but getting one of those is the easiest of the three.
Because none of them are a legal requirement to be a citizen, each one has multiple document set requirements, and if you have the other two, the third is trivial to obtain.
The documents you need if you’re not leveraging another form of ID are basically a set of documents that aren’t that difficult for your average person to get their own copies of but harder for some one else to forge and claim to be another person