The website explains there are 303,644,061 people in the US.
There are at least 88,799 last names and 5,163 first names in common usage.†
There are 1,518 people with my first name‡ and 972 people with my last name.§
As to how I don't exist?¶
There are 0 people in the U.S. with your exact name. While both names you entered were found in our database, neither was common enough to make it likely that someone in the U.S. has that name.
Just for your own edification, it apparently isn't actually linked to any census records or courthouse filings. They're just going strictly on odds.
†FOOTNOTE (crossed): They didn't explain exactly what they mean by "common usage." That there are at least two people who have that name? That more than 2% of the population has that name? And did they count the Anne Heche character on "Men in Trees," a show I watch for the sheer thrill of hearing a TiVi character say, "Marin, I'm worried about you"?
‡FOOTNOTE (double-crossed): more than 99.99% are female. For the record, I know a male Marin.
§FOOTNOTE (swerved): Proving once and for all that my last name is even weirder than my first name.
¶FOOTNOTE (paragraphed): And I quote.