Why is people the plural of person?

[Opus1]

OED doesn’t give any help. Both are distinct words with normal plurals in their own right: Person=individual. Pl. is persons. People = race or group of people (e.g., the Scottish people). Pl. is peoples (the peoples of Southern Africa). So why is people the standard plural of person outside of documents and legal settings, and when did this come about?

[Mandarax]

From World Wide Words:

The words people and person derive from different Latin roots, the former from populum, referring to the people in the sense of the populace, the latter from persona, ‘an actor’s mask; a character in a play’ and which in the English form person came to refer to an individual human being.
…
The normal plural of person was persons, as in “two persons were present”. However, there is evidence from Chaucer onwards that some writers chose to use people as a plural for person, not only in the generalised sense of ‘an uncountable or indistinct mass of individuals’ but also in specific countable cases (Chaucer wrote of “a thousand people”). This began to be questioned in Victorian times, and the pseudo-rule grew up that the plural of person is persons when a specific, countable number of individuals is meant, but that people should be used when the number is large or indefinite.