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.
The US government has the information, but there’s no way for companies to sell you something if they used that data.
It’s the same with US taxes. The IRS knows exactly how much you owe them each year. As a citizen, you cannot access that information. You have to fill out needlessly complicated forms to guess the correct amount of money to send them. If you guess wrong you can go to jail or be fined. To prevent this, you pay a company to fill out those forms. They don’t get access to the correct number either, but you can buy insurance from them so they’ll pay for your lawyer to defend you if you guess wrong.