It's a legal (or pseudo-legal) tic, based on a formal grammatical rule that "people" refers to a large mass (such as the "people of the United States"), and "pe

It's a legal (or pseudo-legal) tic, based on a formal grammatical rule that "people" refers to a large mass (such as the "people of the United States"), and "persons" refers to a finite body of, er, people. Technically, the plural of "person" is "persons," not "people," as the two terms share distinct Latin roots: persona vs. populus, the former referring to a physical person, and the latter to a sociocultural grouping (e.g., SPQR -- Senatus Populusque Romanus, "the Senate and People of Rome"). But we are more likely these days to use "people" as the proper plural of "person," and generally only encounter "persons" in more formal contexts.